Apparatus and Method for the Electrolysis of Water

ABSTRACT

An apparatus for the electrolytic splitting of water into hydrogen and/or oxygen, the apparatus comprising: (i) at least one lithographically-patternable substrate having a surface; (ii) a plurality of microscaled catalytic electrodes embedded in said surface; (iii) at least one counter electrode in proximity to but not on said surface; (iv) means for collecting evolved hydrogen and/or oxygen gas; (v) electrical powering means for applying a voltage across said plurality of microscaled catalytic electrodes and said at least one counter electrode; and (vi) a container for holding an aqueous electrolyte and housing said plurality of microscaled catalytic electrodes and said at least one counter electrode. Electrolytic processes using the above electrolytic apparatus or functional mimics thereof are also described.

This invention was made with government support under Contract NumberDE-AC05-000R22725 between the United States Department of Energy andUT-Battelle, LLC. The U.S. government has certain rights in thisinvention.

FIELD OF THE INVENTION

The present invention relates, generally, to the field of hydrogen andoxygen gas production, and particularly, to water electrolysis devicesand methods of use.

BACKGROUND OF THE INVENTION

Hydrogen gas, in particular, is used in vast quantities for numerousindustrial applications. The demand for hydrogen is increasing,particularly as hydrogen is increasingly being pursued as an ideal fuelsource.

By far, the most common processes for producing hydrogen gas involve thereaction and breakdown of fossil fuels. Some examples of these types ofprocesses include steam reforming of natural gas and coal gasification.However, these processes have the significant disadvantages of relyingon a non-renewable and polluting resource. In particular, largequantities of carbon monoxide and carbon dioxide are generally producedin fossil fuel-based methods for hydrogen production. Accordingly, thereis considerable interest in finding cleaner methods for the large-scaleproduction of hydrogen.

One possible alternative method is the electrolysis of water. Theelectrolysis of water produces hydrogen and oxygen gas without theproduction of toxic and environmentally unfriendly byproducts. Moreover,since the electrolytic method uses electricity as the power source,another advantage of the electrolytic process over hydrocarbon processesis its amenability in receiving electrical power from a renewablesource, such as solar, wind, or hydroelectric power. Some patentreferences directed to electrolysis technology include, for example,U.S. Pat. Nos. 7,601,308, 7,550,068, 7,510,633, 7,459,065, 7,452,449,7,270,908, 7,241,950, 6,855,450, 6,613,215, 5,968,325, 5,667,647,5,665,211, 5,534,120, 5,268,081, 5,089,107, 5,037,518, and 4,737,249,and U.S. Application Publication Nos. 2010/0206722, 2010/0101941,2009/0325014, and 2008/0264780.

The electrolysis of water involves the decomposition (i.e., “splitting”)of water into oxygen and hydrogen gas by the action of an electricvoltage (i.e., current) being applied to the water across electrodes ofopposite polarity. Hydrogen is produced at the negative electrode(cathode) and oxygen is produced at the positive electrode (anode), asshown by the following well-known chemical equations:

Cathode (reduction): 2H⁺(aq)+2e⁻→H₂(g)

Anode (oxidation): 2H₂O(I)→O₂(g)+4H⁺(aq)+4e⁻

Although the electrolytic process has the advantage of more cleanlyproducing hydrogen and is amenable to being powered by renewablesources, the electrolytic process remains non-competitive withconventional hydrocarbon processes because of the labor-intensive andmaterials cost of conventional electrolyzers as well as the prohibitivecost of current precious metal electrodes (e.g., complex platinum platesor honeycombs) used in electrolyzers of the art. Therefore, sincehydrogen can be produced more affordably from fossil fuels, electrolyticprocesses for producing hydrogen have generally been limited tosmall-scale operations.

Yet, it has been estimated that in a future hydrogen economy,electrolyzers 10 to 100 times the size of today's largest units would beneeded (Ivy, J., “Summary of Electrolytic Hydrogen Production”, NationalRenewable Energy Laboratory, NREL/MP-560-36734.). Moreover, suchlarge-scale electrolyzers would be greatly beneficial at the presenttime to take the place of existing hydrogen production technologies.Clearly, state-of-the-art electrolysis technology is significantlydeficient in producing such large-scale amounts of hydrogen and oxygenin a clean and cost-effective manner.

SUMMARY OF THE INVENTION

In a first aspect, the invention is directed to an apparatus for theelectrolytic splitting of water into hydrogen and/or oxygen gas. In someembodiments, the electrolytic apparatus described herein makes use of aplurality of microscaled catalytic electrodes (i.e., microelectrodes) ona surface. In other embodiments, functional mimics of microelectrodes(e.g., a distribution of catalytic hot spots) are used on a bulkelectrode to achieve the same or similar benefits provided by an arrayof microelectrodes. The microscaled catalytic electrodes or functionalmimics thereof can function as cathodes (i.e., where hydrogen isproduced), or anodes (i.e., where oxygen is produced). In particularembodiments, each of the microscaled electrodes is independentlyaddressable, i.e., independently powered, adjusted, and/or monitored.

In a first particular embodiment, the electrolytic apparatus includes:(i) at least one lithographically-patternable substrate having asurface; (ii) a plurality of microscaled catalytic electrodes embeddedin the surface, wherein the microscaled catalytic electrodes are eithercatalytic anode electrodes or catalytic cathode electrodes; (iii) atleast one counter electrode in proximity to but not on the surface,wherein the counter electrode includes at least one catalytic cathodeelectrode if the microscaled catalytic electrodes are catalytic anodeelectrodes, or the counter electrode includes at least one catalyticanode electrode if the microscaled catalytic electrodes are catalyticcathode electrodes; (iv) means for collecting evolved hydrogen and/oroxygen gas; (v) electrical powering means for applying a voltage acrossthe plurality of microscaled catalytic electrodes and the at least onecounter electrode; and (vi) a container for holding an aqueouselectrolyte and housing the plurality of microscaled catalyticelectrodes and the at least one counter electrode.

In a second particular embodiment, the electrolytic apparatus includes:(i) a first lithographically-patternable substrate having a firstsurface, and a plurality of microscaled catalytic anode electrodes onthe first surface; (ii) a second lithographically-patternable substratehaving a second surface, and a plurality of microscaled catalyticcathode electrodes on the second surface; (iii) means for collectingevolved hydrogen and/or oxygen gas; (iv) electrical powering means forapplying a voltage across the plurality of microscaled catalytic anodeand cathode electrodes; and (v) a container for holding an aqueouselectrolyte and housing the plurality of microscaled catalytic anode andcathode electrodes. In further embodiments, the microscaled catalyticanode and cathode electrodes are not separated by an ion-permeablebarrier. In other embodiments, the microscaled catalytic anode andcathode electrodes are separated by an ion-permeable barrier.

In a third particular embodiment, the electrolytic apparatus includes:(i) at least one rigid planar substrate made of a semiconductingcomposition, the at least one rigid planar substrate having a firstsurface, and a second surface opposite the first surface; (ii) aplurality of microscaled catalytic anode electrodes disposed on thefirst surface; (iii) a plurality of microscaled catalytic cathodeelectrodes disposed on the second surface; (iv) at least one poreconnecting the first and second surfaces; (v) electrical powering meansfor applying a voltage across the plurality of microscaled catalyticanode and cathode electrodes; (vi) a first compartment that surroundsthe microscaled catalytic anode electrodes while excluding themicroscaled catalytic cathode electrodes; (vii) a second compartmentthat surrounds the microscaled catalytic cathode electrodes whileexcluding the microscaled catalytic anode electrodes, and (viii) meansfor collecting evolved hydrogen and oxygen gases. In the foregoingembodiment, the rigid planar substrate functions as a common walladjoining (i.e., separating) the first and second compartments.

In a fourth particular embodiment, the electrolytic apparatus includes:(i) at least one first rigid planar substrate made of a semiconductingcomposition, the at least one first rigid planar substrate having afirst planar surface on which a plurality of microscaled catalyst anodeelectrodes are disposed, and a second planar surface opposite to thefirst planar surface; (ii) at least one second rigid planar substratemade of a semiconducting composition, the at least one second rigidplanar substrate having a first planar surface on which a plurality ofmicroscaled catalytic cathode electrodes are disposed, and a secondplanar surface opposite to the first planar surface; (iii) a protonexchange (or polyelectrolyte) membrane (PEM) having first and secondplanar surfaces and sandwiched between the first and second rigid planarsubstrates, wherein the first planar surface of the membrane is inphysical contact with the second planar surface of the first rigidplanar substrate, and the second planar surface of the membrane is inphysical contact with the second planar surface of the second rigidplanar substrate; (iv) at least one pore having a first section and asecond section, wherein the first and second pore sections are colinear,and the first pore section extends from the membrane to the first planarsurface of the first rigid planar substrate, and the second pore sectionextends from the membrane to the first planar surface of the secondrigid planar substrate; (v) electrical powering means for applying avoltage across the plurality of microscaled catalytic anode and cathodeelectrodes; (vi) a first compartment that surrounds the microscaledcatalytic anode electrodes while excluding the microscaled catalyticcathode electrodes; (vii) a second compartment that surrounds themicroscaled catalytic cathode electrodes while excluding the microscaledcatalytic anode electrodes, and (viii) means for collecting evolvedhydrogen and oxygen gases. The foregoing fourth embodiment is generallydepicted in FIGS. 7A and 7B. FIGS. 7A and 7B are meant to be exemplary,and hence, non-limiting to the fourth embodiment. Numerous modificationsand adjustments can be made to the embodiments shown in FIGS. 7A and 7B.In the foregoing embodiment, the planar substrate/PEM membranecombination functions as a common wall adjoining (i.e., separating) thefirst and second compartments. One method of implementing the electricalpowering means in (v) utilizes the 3D microchip stacking technique“through via technology” described in U.S. Pat. Nos. 7,683,459 and7,633,165.

A first particular advantage provided by the instant electrolytic systemis the significantly reduced amount of electrocatalytic precious metalneeded, as compared to bulk precious metal electrodes, for producing anequivalent amount of hydrogen or oxygen. A second particular advantageprovided by the instant electrolytic system is, in particularembodiments, the ability to dispense with a proton-conducting membrane(i.e., proton-exchange or polymer-electrolyte membrane) or any barrierthat functions to separate the anode and cathode or place the anode andcathode in separate compartments. A third particular advantage providedby the instant electrolytic system is the ability of the system tomaintain efficient production of hydrogen and oxygen gas even if one ora certain number of microscaled electrodes fails. A fourth particularadvantage provided by the instant electrolytic system is the ability ofthe system to be significantly scaled up by increasing the number ofmicroscaled electrodes, and this, in a cost-effective and efficientmanner by the use of photolithographic methods for patterning largenumbers of the microscaled electrodes on a suitable substrate.

In a fifth particular embodiment, the electrolytic apparatus includes:(i) a bulk catalytic electrode containing thereon a plurality ofmicroscopic catalytic hot spots on a surface of the bulk catalyticelectrode, wherein the bulk catalytic electrode is either a catalyticanode or catalytic cathode; (ii) a counter electrode; (iii) means forcollecting evolved hydrogen and/or oxygen gas; (iv) electrical poweringmeans for applying a voltage across the bulk catalytic electrode andcounter electrode; and (v) a container for holding an aqueouselectrolyte and housing the bulk catalytic electrode and counterelectrode.

In a sixth particular embodiment, the electrolytic apparatus includes:(i) a bulk catalytic electrode having on its surface an insulating layercontaining a plurality of microscopic holes therein, wherein the bulkcatalytic electrode is either a catalytic anode or catalytic cathode,and the holes permit the bulk catalytic electrode to be exposed toelectrolyte only at the holes; (ii) a counter electrode; (iii) means forcollecting evolved hydrogen and/or oxygen gas; (iv) electrical poweringmeans for applying a voltage across the bulk catalytic electrode andcounter electrode; and (vi) a container for holding an aqueouselectrolyte and housing the bulk catalytic electrode and counterelectrode.

In another aspect, the invention is directed to an efficient method forproducing hydrogen and/or oxygen gas by processing an aqueouselectrolyte with any of the electrolytic systems described above. Inparticular embodiments, the electrolytic system is electrically poweredby a renewable energy source or a source of electricity that isgenerated by nuclear power. In the case of nuclear electricity, theexcess or byproduct heat, such as provided in the operation of a nuclearpower plant can be used in conjunction with theelectrolytically-produced hydrogen and oxygen for certain fuel-producingmanufacturing operations. For example, the method described above forproducing hydrogen and/or oxygen gas is coupled to a process thatutilizes hydrogen or oxygen gas (e.g., a Fischer-Tropsch, Haber process,or petroleum refining process).

In yet another aspect, the invention is directed to a method forproducing chlorine and/or a metal hydroxide by a chloralkali process.The chloralkali process involves processing an aqueous metal-chloridesalt electrolyte with any of the electrolytic systems described abovesuch that chlorine gas is produced at the anode side of the electrolyzerand hydrogen gas and a metal hydroxide are produced at the cathode sideof the electrolyzer. In particular embodiments, the chloralkali processdescribed above is electrically powered by a renewable or nuclear energysource. In other particular embodiments, the chloralkali processdescribed above is coupled to a process that utilizes chlorine gasand/or a metal hydroxide.

In particular embodiments, some of the objects of the present inventioninclude: a method and apparatus for the electrolysis of water in whichhydrogen and oxygen are produced on opposite sides of an electroactivebarrier (or membrane), wherein the sides are patterned with one or moreelectrolytic electrodes; a means for maintaining electroneutrality via aproton or ion channel; a means for sending power to the electroactivebarrier via wireless telemetry, for example, for actuating theelectrolytic electrodes; a means for bidirectional information transfervia wireless telemetry, for example, that sends command information tothe individual electrodes of the electroactive membrane and receivesstatus and operational information from the electrodes. Further andother objects of the present invention will become apparent from thedescription contained herein.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1 a, 1 b. Drawings depicting an exemplary water electrolysisdevice. FIG. 1 a is an overall conceptual view. FIG. 1 b is a moredetailed view of a specially fabricated silicon wafer electrode assemblyembedded in a common wall (FIG. 1 a) between hydrogen and oxygencompartments.

FIG. 2. Illustration depicting a proton-conducting pore in relation tothe electrodes.

FIG. 3. Schematic showing an exemplary process in the preparation of amicroelectrode-pore system on a semiconducting substrate. Step 1,semiconducting substrate; Step 2, lithographically define and etchpores; Step 3, oxidize semiconducting wafer, or atomic layer deposition;Step 4, evaporate metal, i.e., lithographically define or shadow.

FIGS. 4 a, 4 b. Illustrations depicting an exemplary apparatus usingwire electrodes for testing the utility of the invention (low crossmigration of H₂ and O₂. See FIG. 1 for additional perspective.

FIG. 5. Illustration depicting an exemplary arrangement ofmicroelectrodes, traces, bond pads and pores on a substrate (only oneelectrode, trace and bond pad are shown for the sake of clarity).

FIG. 6. Perspective view of an embodiment in which a silicon wafercontaining at least one microelectrode on each side is sealed in thewall of a dual gas-collection tube.

FIGS. 7 a, 7 b. FIG. 7 a, exploded view, depicts an embodiment in whicha wafer-electrode assembly includes a PEM membrane sandwiched betweentwo silicon wafers. In one embodiment, the electrical powering means forperforming electrolysis utilizes through-silicon via technology. FIG. 7b is an assembled view of the wafer electrode assembly sandwich-likestructure.

FIG. 8. Simplified view showing how hydrogen may be collected when it isproduced in the interior of a tubular structure.

FIG. 9. Illustration showing a possible arrangement of transmitting andreceiving coils when the plane of the receiving coil is parallel to theplane of the wafer.

FIG. 10. Perspective illustration of a silicon wafer electrode assemblytest structure, with photolithographed electrodes and etched pores, usedfor obtaining test data.

FIG. 11. Exploded view of test apparatus using a silicon wafer electrodeassembly. Separate streams of hydrogen and oxygen are produced onopposite sides of the wafer.

FIG. 12. Graph showing rate of electrolytic hydrogen and oxygenproduction from photolithographic patterned nickel microelectrodes onboth sides of a four inch silicon wafer when an electrolytic current of500 μA was discharged through a microelectrode cathode/anode pair.

FIG. 13. Graph showing rate of electrolytic hydrogen and oxygenproduction from photolithographic patterned nickel electrodes on bothsides of a four inch silicon wafer when an electrolytic current of 1000μA on a single microelectrode is used.

FIG. 14. Graph showing rate electrolytic hydrogen and oxygen productionfrom movable platinum wire electrodes butting up against the oppositesides of a silicon wafer containing patterned pores without patternedmicroelectrodes on the surface of the wafer.

FIG. 15. Graph showing electrolytic rate of hydrogen and oxygenproduction from a two-chamber test cell with no barrier between theelectrodes.

FIG. 16. Illustration depicting an electrolytic system according to anembodiment of the invention corresponding to the data of FIG. 15 with nomembrane or barrier between the electrodes, i.e., a membranelesselectrolytic system.

FIG. 17. Illustration of an embodiment of the membraneless electrolyticsystem corresponding FIG. 16, and further including canopy gascollection devices.

DETAILED DESCRIPTION OF THE INVENTION

In one aspect, the invention is directed to an apparatus (i.e.,electrolyzer) for the electrolytic splitting of water into hydrogenand/or oxygen. In most embodiments, the electrolyzer produces bothhydrogen (at the cathode) and oxygen (at the anode) in stoichiometric ornear-stoichiometric amounts. However, under particular conditions knownin the art, the electrolyzer may produce another gas or chemical inplace of, or in addition to, either hydrogen or oxygen (e.g., thechloralkali process in which chlorine gas is predominantly produced atthe anode).

In particular embodiments, the electrolyzer includes at least onelithographically-patternable substrate (i.e., substrate) having asurface upon which a plurality of microscaled catalytic electrodes(i.e., microelectrodes or electrodes) are embedded. By being “embedded”into the surface is meant that the electrodes are attached or within thesubstrate surface provided that the electrocatalytic portion of theelectrode is exposed so that it can make contact with the aqueouselectrolyte during operation.

In other particular embodiments, the microelectrodes are embedded intothe surface by lithographic patterning of the microelectrodes onto thesubstrate. Lithographic patterning includes any process by which apattern is constructed on a surface, e.g., physical lithography (e.g.,stamping), photolithography, and other forms of lithography.Photolithographic processes, in particular, are particularlyadvantageous in that they have the ability to deposit large numbers ofelectrodes onto a substrate in a short period of time and in acost-effective manner. Any of the lithographic (particularlyphotolithographic) patterning processes of the art used forsemiconductor device fabrication and fabrication of integrated circuitscan be used for imprinting the microelectrodes onto the substrate. Inparticular embodiments, the microelectrodes are imprinted by physical orchemical vapor deposition (i.e., PVD or CVD), electroplating,electroless plating, or sputtering deposition of the electroactive metalfollowed by a lift off, etching, or standard lithography/etch processknown in the art. The etching process can be, for example, a surfacemicromachining or high aspect ratio micromachining (i.e., deepreactive-ion etch) process. In some embodiments, the lithographic methodemploys a photomask or reticle to lay down the pattern, while in otherembodiments (e.g., in electron beam lithography) a mask may not be used.See, for example, W. M. Moreau, Semiconductor Lithography: Principles,Practices, and Materials (Microdevices), Springer, 1^(st) Ed., 1987, andC. A. Mack, Fundamental Principles of Optical Lithography: the Scienceof Microfabrication, Wiley, 2008, both of which comprehensively describea range of lithographic techniques that can be used herein forpatterning of microelectrodes and associated wiring and electronics on asubstrate. The contents of W. M. Moreau and C. A. Mack are hereinincorporated by reference in their entirety.

In particular embodiments, the microelectrodes are deposited by any ofthe modified semiconductor device fabrication technologies employed inmanufacturing microelectromechanical systems (MEMS) devices, nowwell-established in the art. The microelectrodes of the instantinvention can include a variety of specialized electronic componentsother than bonding pads and wiring. Some examples of specializedelectronic components include microsensors, data processing units, andmicroprocessors. Other specialized components include an electricfeedthrough means (e.g. “through vias”), perpendicular to the plane ofthe wafer, which facilitates the application of a voltage to a cathodeand anode pair located on opposite sides of the wafer. MEMSmanufacturing processes can include any of a variety of techniques, suchas, for example, molding, plating, wet etching, dry etching (e.g., RIEand DRIE), and electrical discharge machining (EDM), all of which areuseful for imprinting a range of miniaturized electronic components.

In other particular embodiments, the microelectrodes are deposited by aconductive ink printing process. In the ink printing process, adepression (e.g., channel, groove, or complex features) is made in thesubstrate surface. The features of the depression can be made by, forexample, a stamping die or roller. The depression is then filled in witha conductive ink, such as a conductive polymer or metal-containing inkThe metal-containing ink can include the metal or conductive carbon inany suitable form, such as metal particles or precursor compound.Generally, after deposition of the metal-containing ink, the ink-coatedsubstrate is post-treated under conditions (e.g., a heating orirradiation step) that removal solvent and cause the metal particles ormetal precursor to fuse and form conducting features. The features, onceproduced, may be amplified or appropriately modified by deposition ofadditional metal by other means, such as electrolytic or electrolessplating. The details of a typical ink printing process is found, forexample, in U.S. Application Pub. No. 2009/0061213, the contents ofwhich are incorporated herein by reference in their entirety.

The substrate can be any of the lithographically-patternable substratesknown in the art. In many embodiments, the substrate has asemiconducting composition (e.g., as used in the manufacture ofintegrated circuits, microchips, and MEMS devices). Commonly, thesemiconducting substrate is rigid, such as a silicon-containingsubstrate (e.g., silicon or silicon carbide), germanium, galliumarsenide, gallium nitride, indium arsenide, indium phosphide, boronnitride, or a combination thereof, and crystalline, polycrystalline,amorphous, and p- and n-doped versions thereof. Although the examplesgiven above are all inorganic in composition, the semiconductingsubstrate can be or include an organic semiconducting composition. Someexamples of organic semiconducting materials includepolyphenylenevinylene, polyacetylene, polypyrrole, and polyaniline. Inother embodiments, particularly in the case of an organic semiconductingsubstrate, the substrate can be non- rigid (i.e., flexible). In someembodiments, one or more of the above classes or specific types ofsubstrates are excluded as a substrate material.

In particular embodiments, the substrate is silicon. The silicon can bein any suitable form, such as crystalline, polycrystalline, oramorphous. The silicon can also be p-doped (e.g., with boron) or n-dopedtype (e.g., with phosphorus) or a combination thereof. Multilayeredforms of silicon are also contemplated, as are multilayer substratescontaining one or more layers of silicon and one or more layers of asemiconducting or non-conducting composition, including 3D sandwich-likestructures in which a PEM membrane is bonded between two silicon wafersusing through-silicon via technology.

In yet other embodiments, the substrate is, or includes, an insulating(i.e., low-conducting or non-conducting) composition amenable to thedeposition or embedding of microelectrodes therein, preferably by alithographic process. The insulating composition, can be, for example, arigid or flexible polymer, a ceramic, or a hybrid organic-inorganicmaterial. For the purposes of the instant invention, the substratematerial is preferably insoluble in, and non-reactive with, water andaqueous electrolytes, particularly their alkalinized forms. Someexamples of insulating polymers include, for example, polyethylene,polypropylene, polymethyl methacrylate (PMMA), polycarbonate,polyvinylchloride (PVC), silicones, polyimides, and the fluoropolymers,such as polytetrafluoroethylene (PTFE), fluorosilicones, andfluoroelastomers. Some examples of ceramic materials include the metaloxides (e.g., titanium oxide, silicon oxide, and indium tin oxide),silicates, aluminates (e.g., alumina), and aluminosilicates. Someexamples of hybrid organic-inorganic materials include hybrid sol-gel(e.g., ormosil) and metal oxide framework (MOF) materials. In someembodiments, one or more of the above classes or specific types ofsubstrates are excluded as a substrate material.

The substrate can have any suitable shape, such as a filled (i.e.,non-hollow) cuboidal, bulbous, or spherical type of shape. However, morecommonly, the substrate considered herein has a flat (i.e., planar)shape. The planar substrate can have angled or curved edges. Moreover,the planar substrate can be in the form of a flat (i.e., straight) sheetor in the form of a rolled, cylindrical, or helical sheet. The planarsubstrate may also be formed into a polyhedral shape, such as a hollowbox or multisided column. Regardless, the planar substrate possesses atleast two surfaces, i.e., a first and a second planar surface. Unlessotherwise indicated, the planar surfaces considered herein are thosehaving the larger surface areas as compared to edge surfaces of theplanar substrate. Generally, the microelectrodes are embedded intoeither or both of the planar surfaces of a planar substrate.

The planar substrate can have any suitable thickness, including any ofthe thicknesses available in silicon wafers commonly used insemiconductor device fabrication. In particular embodiments, the planarsubstrate has a thickness of precisely, about, less than, up to, orgreater than, for example, 1, 2, 3, 4, 5, 10, 15, 20, 25, 30, 35, 40,45, 50, 60, 70, 80, 90, 100, 150, 200, 250, 300, 350, 400, 450, 500,550, 600, 650, 700, 750, 800, 850, 900, 950, or 1000 microns (μm), or athickness within a range bounded by any two of the foregoing exemplaryvalues. The diameter of the planar substrate (i.e., longest distanceacross a planar surface) can be of any size that can properly fit intothe container of the electrolyzer while not becoming a significantimpediment to the electrolysis process. Generally, particularly in thecase of silicon wafers, the diameter varies from one or two inches(i.e., 25 or 50 mm) up to 18 inches (i.e., ˜450 mm). Particularly in thecase of silicon wafers, the thickness of the silicon wafer generallyincreases with increasing diameter.

In some embodiments, a first planar surface of a planar substratecontains anode or cathode microelectrodes embedded therein while thesecond planar surface of the planar substrate (opposite to the firstplanar surface) does not contain anode or cathode microelectrodesembedded therein or disposed thereon in any manner. In otherembodiments, a first and second planar surface of a planar substrateeach contains microelectrodes embedded therein or disposed thereon. Themicroelectrodes on the first planar surface may have the sameconstruction as microelectrodes on the second planar surface,particularly when the microelectrodes on both surfaces are expected toperform the same function (i.e., as anodes or as cathodes). However, ininstances where microelectrodes on each planar surface of a planarsubstrate are desired to perform different functions (e.g., cathodemicroelectrodes on one side and anode microelectrodes on the oppositeside), they may all be of the same construction but operated differentlyso that they perform different functions. In particular embodiments, themicroelectrodes embedded in the second planar surface are counterelectrodes to the microelectrodes on the first planar surface, and themicroelectrodes on the first planar surface have a different or sameconstruction (e.g., different or same electrocatalytic material) thanthe counter electrodes.

The microelectrodes of the instant invention have at least onemicroscale dimension. For example, one, two, or all of the dimensions ofthe microelectrodes can be microscale. In different embodiments, the atleast one microscale dimension is precisely, about, less than, or up to,for example, 1, 2, 3, 4, 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 60, 70,80, 90, 100, 150, 200, 250, 300, 350, 400, 450, 500, 550, 600, 650, 700,750, 800, 850, 900, 950, 1000, 1100, 1200, 1300, 1400, 1500, 2000, 2500,3000, 3500, 4000, 4500, or 5000 microns (μm), or a size within a rangebounded by any two of the foregoing exemplary values. In particularembodiments, the microelectrode has at least one microscale dimension ofat least 10, 20, 30, 40, 50, 60, 70, 80, 90, or 100 microns and up to200, 300, 400, 500, 600, 700, 800, 900, 1000, 1500, or 2000 microns.

The microelectrodes contain at least one electrocatalytic metal (i.e.,catalytic metal) effective as a cathode or anode material in a waterelectrolysis system. The catalytic metal can be any of the metals knownin the art having this property. Some examples of catalytic electrodemetals include platinum, palladium, nickel, gold, tungsten, ruthenium,molybdenum, tantalum, cobalt, iron, and carbon, as well as compositesand alloys thereof, such as platinum-coated titanium or platinum-nickelalloy, respectively. In some embodiments, the anode and cathodeelectrodes have the same electrocatalyst composition, while in otherembodiments, the anode and cathode electrodes have differentcompositions.

The electrocatalyst composition of either the anode, cathode, or both,may be appropriately modified to adjust the reactivity of the electrode,such as by making one or both of the electrodes able to produce aspecies other than hydrogen or oxygen. For example, if chlorineproduction is desired by the chloralkali process, anode microelectrodesmay be modified to include a more non-reactive electrode material, suchas titanium or carbon. Alternatively, when adapting the electrolyticprocess to a chloralkali process, the anode microelectrodes may beconstructed of a non-reactive (i.e., non-catalytic) material useful inproducing more chlorine than oxygen, while the cathode microelectrodescontain a catalytic material more suitable for producing hydrogen andmetal hydroxide. Other applications, such as reduction of carbondioxide, can be achieved by including one or more non-reactive metals inthe electrocatalytic composition.

The microelectrodes may further include a coating (e.g., MnO₂) forincreasing the operational stability, Faradaic efficiency, or corrosionresistance of the electrode. The electrocatalytic portion of themicroelectrodes may also be formed in situ, such as by the in situformation of an oxygen-evolving catalyst in water containing phosphateand Co⁺² ions (Kanan, M. W., and Nocera, D. G. (2008), Science, 321, pp.1072-1075). The microelectrodes may further be hermetically sealed, bymethods known in the art, provided that electrocatalytic (i.e., active)surfaces of the microelectrodes are exposed (i.e., accessible to theaqueous electrolyte).

In some embodiments, the electrocatalytic portion of the microelectrodeis non- porous (i.e., smooth or continuous). In other embodiments, theelectrocatalytic portion of the microelectrode is porous, rough, orcorrugated. The porosity can correspond to a pore volume of or at least,for example, 5, 10, 20, 30, 40, 50, 60, 70, or 80 volume percent, or apore volume within a range between any two of these values.

The term “plurality of microelectrodes”, as used herein, indicates, inits most basic sense, at least two microelectrodes. However, as theinstant invention is particularly focused on the large scale productionof hydrogen and oxygen, a “plurality of microelectrodes” is herein moretypically defined as at least 5, 10, 20, 30, 40, 50, 100, 200, 300, 400,500, 1,000, 2,000, 3,000, 4,000, 5,000, 10,000, 20,000, or 50,000microelectrodes or cathode/anode pairs per total surface area of asubstrate surface, or per a specific area (e.g., per cm²) of thesubstrate surface.

The plurality of microelectrodes described above are in proximity to atleast one counter electrode, provided that the at least one counterelectrode is not on the same surface as the plurality ofmicroelectrodes. In particular embodiments, the counter electrode refersto a plurality of counter microelectrodes. By being a counter electrode,the counter electrode is designed to function in a polarity opposite ofthe microelectrodes. For example, if the microelectrodes are cathodes,the at least one counter electrode functions as an anode, andconversely, if the microelectrodes are anodes, the at least one counterelectrode functions as a cathode. In some embodiments, themicroelectrodes and counter electrode contain the same electrocatalyticmaterial. By being in “proximity to” is meant that the microelectrodesand at least one counter electrode are close enough to efficientlyconduct protons and/or other ionic species between each other (i.e.,across an electrolyte). Typically, the microelectrodes and at least onecounterelectrode are also in electrical communication. However, theinstant invention includes the possibility that the anode and cathode,together in a common electrolyte, are each engaged in separateelectrical circuits with other counter electrodes not in the commonelectrolyte.

In a first set of embodiments, the counter electrode includes one ormore bulk electrocatalytic anodes or cathodes of the art. The bulkelectrocatalytic anode or cathode of the art can have any of thecompositions, as described above, as well as any suitable size, shape,or other physical characteristics.

In a second set of embodiments, the counter electrode is or includes aplurality of microelectrodes, i.e., a second plurality ofmicroelectrodes that are counter electrodes to a first plurality ofmicroelectrodes described above. The plurality of microelectrodes of thecounter electrode (i.e., counter microelectrodes) can have any of thecompositional and physical characteristics described above for the firstplurality of microelectrodes.

Furthermore, the plurality of microelectrodes of the counterelectrodecan be embedded in a second surface, which is a surface different fromthe first surface on which the first plurality of microelectrodes areembedded. In one embodiment, the second surface on which the pluralityof counter microelectrodes are embedded is not located on the substrate(i.e., first substrate) on which the first plurality of microelectrodesare embedded, i.e., the plurality of counter microelectrodes areembedded in one or more surfaces of a second substrate, wherein it isunderstood that the first and second substrates are different (i.e.,separate and not attached). In another embodiment, the second surface onwhich the plurality of counter microelectrodes are embedded is locatedon a different surface but on the same substrate on which the firstplurality of microelectrodes are embedded. For example, in particularembodiments, the substrate is a planar substrate having a first planarsurface and a second planar surface (i.e., first and second sides)opposite to each other, wherein the first planar surface contains aplurality of microelectrodes thereon, and the second planar surfacecontains a plurality of counter electrodes thereon. As used herein, theterm “same substrate” can refer to a single continuous (i.e., seamless)substrate, or alternatively, to two or more substrate portions connectedor bonded to each other. In some instances, one or more gaps may existbetween the substrate portions, and the substrate portions attached byone or more connection or bond points.

As known in the art, in order for a water electrolyzer to functionproperly, means need to be included to prevent hydrogen and oxygen gasesfrom mixing, while selectively allowing the movement of protons and/orother ionic species from the anode to the cathode. Conventional practicein the art has been to include an ion-conducting material (e.g., aproton exchange membrane) for this purpose. Although an ion-conductingmaterial can also be used in the instant invention, the electrolyticapparatus described herein can advantageously dispense with anion-conducting or ion-permeable material altogether. Thus, in particularembodiments of the instant invention, a plurality of microelectrodes anda counter electrode (which can be a plurality of countermicroelectrodes), both held on separate substrates, are not separated byany means, i.e., an ion-permeable or ion-conducting barrier is notincluded. Although other non-partitioning features, such as microfluidicchannels, may be included in some embodiments to modify or aid the flowbetween anode and cathode compartments, the foregoing barrier-lessembodiment generally excludes any such feature or other feature placedbetween the anode and cathode, other than the electrolyte itself.

Reference is made to FIGS. 16 and 17 in which a barrier-less embodimentis depicted. As shown in FIGS. 16 and 17, two electrode systems ofopposite polarities are in close proximity and in a common electrolytewithout an ion-permeable barrier between the electrode systems. Eachelectrode system is depicted as a cylindrical substrate on which areembedded microelectrodes, as represented by the indicated dots. A meansfor collecting produced hydrogen and/or oxygen is necessary during theelectrolytic process. The means can be any such means, such as a simplepartitioning device held above one or both of the electrode systems,such as the canopies depicted in FIG. 17, wherein the partitioningdevice defines or separates gas collecting compartments.

In FIG. 16, electrical contacts 72 are connected by electricallyconducting means 74 to the anodes 14 and cathodes 12. The verticalarrows indicate product gases oxygen and hydrogen rising in laminarflow. Examples of electrically conducing means 74 are conventional wiresor superconducting wires. The latter will minimize resistive heatingloses in transmitting electrical current to the anodes 14 and cathodes12.

In FIG. 17, separate canopies 76 are placed over each of the ensemblesof cathodes and anodes. Each canopy has an outlet tube 78 for collectingtheir respective product gases. The bottom edges of the canopies extendbelow the level of the static electrolyte in the chamber. They definerestricted headspaces in the cathode and anode regions of the apparatus.There is no gas-phase diffusion pathway between the hydrogen and oxygenheadspaces. The only diffusion pathway for dissolved molecular hydrogenand oxygen is in the static electrolyte. It is known in the art that thecharacteristic diffusion times for dissolved hydrogen and oxygenmolecules in static liquid are much longer that the characteristicescape times for gas bubbles ascending in static liquids under theaction of buoyant forces. These principles allow the production ofseparate streams of hydrogen and oxygen with good purity which areremoved from the headspaces via collection tubes 78.

The apparatus described herein is able to operate without anion-permeable membrane or any type of partition primarily by virtue ofthe small size of the microelectrodes, along with careful adjustment ofelectrode currents to be below a threshold current at which hydrogen oroxygen bubbles produced at the electrode surface will burst. Bypreventing bursting, the onset of turbulence in the bulk electrolyte isavoided. The small size of the instant microelectrodes, along withcareful adjustment of electrode currents to be below said thresholdcurrent, produces bubbles that grow at the electrode surface, breakfree, and ascend without bursting by gravitational buoyant force.Preferably, the bubbles rise (i.e., vertically) in a column of static(i.e., non-flowing) liquid. Accordingly, preferably, the aqueouselectrolyte considered herein is not subjected to turbulence, as canoccur under laminar flow conditions.

By preventing the bursting of bubbles and turbulence, hydrogen is slowto reach the vicinity of the anode, while oxygen is slow to reach thevicinity of the cathode. The rate of diffusion of dissolved hydrogen andoxygen in the static electrolyte is much slower than the rate of bubblerise in the column of electrolyte. This large difference in therespective kinetic rates of gas transport ensures production of gasstreams of high purity. Another advantage of the instantly describedbarrier-less (i.e., membraneless) set up is that the anode and cathode,particularly when both include a plurality of microelectrodes, can beheld in close proximity in the absence of any cross-contamination ofgases between electrodes, especially in dense, viscous electrolytes witha low solubility of oxygen, such as 12 M KOH. The close proximity ofanode and cathode is advantageous for the reason that the closer theproximity between anode and cathode, the lower the resistance, and thus,the more energy-efficient the electrolysis system. Generally, a “closeproximity” between anode and cathode indicates a spacing between anodeand cathode electrodes of up to or less than 30 cm, 25 cm, 20 cm, 15 cm,10 cm, 5 cm, 1 cm, or 0.5 cm, or a range of distance between any two ofthe foregoing exemplary values. Particularly when both the anode andcathode sides are both a plurality of microelectrodes, the foregoingexemplary distances or ranges thereof between anode and cathodeelectrodes can refer to nearest electrodes, farthest electrodes, anaverage distance, or range of distances between cathode and anodeelectrodes. During the course of operation of the electrolysis device,the electrolyte will become saturated with dissolved oxygen andhydrogen. The dissolved oxygen will eventually occupy the same physicalspace as the rising hydrogen bubbles from the cathode. However, becauseof the slow process of diffusion of oxygen in a static liquid, thepurity of the produced hydrogen gas is generally at least 90% H₂ and nomore than 10% O₂, or better, as indicated by the data presented herein.In some embodiments, the purity of the produced hydrogen gas is at least95% H₂ with no more than 5% O₂. In yet other embodiments, the purity ofthe produced hydrogen gas is at least 98% or 99% H₂ with no more than 2%or 1% O₂, respectively.

In other embodiments, the anode and cathode electrodes are separated byan ion-permeable (i.e., cation-permeable and/or anion-permeable)barrier. The barrier can be in the form of, for example, a membrane, arigid wall, or baffle. In some embodiments, the ion-permeable barrier isor includes an ion-conducting material, such as any of the cation orproton exchange materials known in the art. The cation or protonexchange material can be, for example, any of the proton conductingionomers or resins known in the art. The ionomers or resins aretypically solids or gels under the operating conditions of theelectrolysis unit. As known in the art, proton-conducting ionomersgenerally include an alkali or alkaline earth metal salt, or a protonicacid or salt thereof, complexed with one or more polar polymers. The oneor more polymers of the proton-conducting ionomer or resin can be, forexample, polyimide, polyether, polysiloxane, or polyester, as well ascombinations, copolymers, and crosslinked versions thereof. Other resinsmay be included in the ion conducting barrier, such as phenolic,phenol-formaldehyde, polystyrene, styrene-divinyl benzene,polyvinylchloride, and fluoropolymer resins.

In yet other embodiments, a porous barrier separates the anode andcathode. In some embodiments, the porous barrier is used in the absenceof a proton- or ion-conducting material. Instead, ion migration ispermitted solely by pores (i.e., channels) present in the barrier. Inorder to allow migration of ions, the pores connect one surface of thebarrier, which faces or contains one of the electrodes, with theopposite surface of the barrier, which faces or contains the counterelectrode.

In some embodiments, the porous barrier contains no microelectrodesthereon, i.e., the porous barrier separates an anode from a cathode heldin two separate compartments, each being a certain distance from theporous barrier. In the foregoing embodiment, the porous barrierfunctions as a common wall adjoining the two separate (i.e., anodic andcathodic) compartments. In other embodiments, the porous barriercontains at least one surface, and a plurality of microelectrodes isembedded on at least one surface of the porous barrier. In particularembodiments, the porous barrier is a planar substrate, as describedabove, containing pores therein, wherein a first planar surface and asecond planar surface of the porous barrier each contain microelectrodesembedded thereon, i.e., microelectrodes are embedded on the first planarsurface and counter microelectrodes embedded on the second planarsurface of the porous barrier.

The pores can have any suitable size (i.e., diameters). In someembodiments, the pores are in the microscale (i.e., micropores). Indifferent embodiments, the micropores have pore diameters of precisely,about, less than, or up to, for example, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10,15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, 100,125, 150, 175, 200, 250, 300, 350, 400, 450, or 500 microns, or a poresize within a range bounded by any two of the foregoing values. In otherembodiments, the pores are in the nanoscale (i.e., nanopores). Thenanopores considered herein have pore diameters less than one micron. Indifferent embodiments, the nanopores have pore diameters of precisely,about, less than, or up to, for example, 1, 2, 3, 4, 5, 10, 20, 30, 40,50, 100, 200, 300, 400, 500, 600, 700, 800, or 900 nm, or a pore sizewithin a range bounded by any two of the foregoing values. In otherembodiments, the pores are in the macroscale (i.e., macropores). Themacropores considered herein have pore diameters above 500 microns. Indifferent embodiments, the macropores have pore diameters of precisely,about, less than, up to, or above, for example, 600 μm 700 μm, 900 μm, 1mm, 2 mm, 4 mm, or 5 mm or a pore size within a range bounded by any twoof the foregoing values. In other embodiments, the pore size is within arange bounded by any two sizes between micropores, nanopores, andmacropores (e.g., 100 nm to 100 μm).

In some embodiments, the pore sizes are moderately or highly uniform byhaving a moderate or low average deviation, such as ±50%, ±40%, ±30%,±20%, ±10%, ±5%, ±2%, or ±1%, or less from a particular pore size (e.g.,10 micron pores within a 10% deviation is equivalent to pores having asize ranging from 9 to 11 microns). In other embodiments, the pore sizesare fairly or highly disperse, such as by including a combination ofmicropores and nanopores, or micropores and macropores, or nanopores andmacropores.

In some embodiments, the porous barrier contains as few as one, two,three, four, or five pores. In other embodiments, the porous barriercontains a greater number of pores, such as, at least 10, 20, 30, 40,50, or 100 pores. In particular embodiments, the porous barrier containsa grid (i.e., pattern) of pores, typically arranged in a fairly orprecisely equidistant manner. The pattern of pores can include hundredsor thousands of pores, or alternatively, a number of pores per area ofthe barrier material (e.g., precisely, at least, or up to 1, 2, 3, 4, 5,10, 20, 30, 40, 50, 100, 200, 500, 1,000, or 5,000 pores per squarecentimeter). Although a small number of pores may be incorporated into asubstrate by macromachining means (e.g., drilling or stamping), a largenumber of pores, such as a pattern, can be more efficiently incorporatedby a lithographic patterning (e.g., microfabrication) process in which areactive ion or acid etch process is also used. Alternatively,particularly if nanopores or micropores are desired, these may beincorporated by the process by which the porous substrate is prepared,e.g., by a supramolecular assembly process (e.g., in the production ofMOFs) or ceramic firing process.

In several embodiments, the pores are open, i.e., not filled with anion-conducting material. In other embodiments, the pores, or a portionthereof, are filled with an ion-conducting material.

The electrolysis apparatus described herein also includes a means forcollecting evolved hydrogen and/or oxygen gas produced by theelectrolytic splitting of water. If a gas other than hydrogen or oxygenis produced (e.g., chlorine), the foregoing means is also capable ofcollecting any such gas, along with any suitable modifications that maybe necessary, such as modification of the walls of the collectingcontainer to be corrosive resistant if a corrosive or reactive gas isproduced. In particular embodiments, the means for collecting evolvedgases includes a tubular or columnar structure positioned over theanodic or cathodic compartment (and specifically, in a position thatwill collect bubbles as they break off from the electrode and rise). Inthe event that both hydrogen and oxygen gas are being separatelycollected, two different tubular or columnar structures can beseparately positioned over each electrode compartment. The foregoingmeans for collecting gas is based on the feature of the instantinvention that bubbles of evolved gas are made to form and break offfrom the electrode without bursting, after which the bubbles risethrough a tube or vertical column to be collected in a holding zone. Theholding zone can be, for example, a storage tank or gas-absorbentmaterial, either of which may be pressurized or unpressurized, andeither cooled or left at ambient temperature.

In some embodiments, the means for collecting evolved gas is a canopytrapping device positioned over the substrate containing a plurality ofmicroelectrodes. FIG. 17 depicts such canopy trapping devices being usedon the electrolytic apparatus depicted in FIG. 16. Referring to FIG. 17,the two electrode systems, each containing a cylindrical substratehaving microelectrodes embedded thereon, have been fitted with canopytrapping devices 76. Each canopy trapping device possesses at least thefeature that the bottom portion (i.e., portion facing toward theelectrode system) is below liquid level and open to allow gas entry,while the top portion (i.e., portion over all of the microelectrodes) isclosed to permit gas trapping. By necessity, the top portion of thecanopy trapping device needs to be above the electrode system in orderto collect all of the evolved gas. In some embodiments, the canopytrapping device is positioned such that the bottom open portion of thetrapping device lies over the entire electrode system and does not coverany of the microelectrodes, while in other embodiments, the canopytrapping device is positioned such that the bottom open portion lies ator below a portion or all of the electrode system, thereby covering aportion or all of the microelectrodes. Other features may beincorporated into or used in combination with the canopy trappingdevices, such as tubes or outlets for transferring the trapped gas.Pressure gauges may also be included for monitoring the levels of gasbeing produced. Furthermore, the shape of the trapping canopy is no waylimited to the cylindrical shape depicted in FIG. 17. For example, insome embodiments, the trapping canopy has the shape of a dome, arectangular tube, or a tiered columnar shape.

In particular embodiments, a substrate material containingmicroelectrodes embedded thereon, as described above, is connected to orfunctions as part of the means for collecting evolved gases. Forexample, in some embodiments, a substrate material containing aplurality of microelectrodes embedded thereon serves as a wall (i.e.,side) or portion thereof of a tube or column that functions to collectan evolved gas. In the foregoing embodiment, the microelectrodes on thesubstrate are necessarily positioned with their catalytically activeportions facing into the collection tube. During operation, the tubetypically also includes the electrolyte in order for gas formation tooccur inside the tube. In a particular arrangement, the substratematerial containing a plurality of microelectrodes embedded thereon isitself embedded in or otherwise disposed on a wall of the gas collectingtube. For example, in some embodiments, one or a plurality of substrates(e.g., silicon wafers), each containing a plurality of microelectrodesembedded thereon, are attached to or embedded in the surface of thecollecting tube or column.

The electrolysis apparatus described above also includes electricalpowering means for providing electrical power to each of the pluralityof microelectrodes and one or more counter electrodes. The electricalpowering means includes all of the features and devices known in the artfor transmitting an electrical current to an electrical device.Generally, for the purposes of the instant invention, several of theelectrical powering features are on the microscale in order to properlyengage each of the microelectrodes. Some examples of features anddevices that are typically included to electrically power themicroelectrodes include wiring and electrical bonding pads, any of whichcan be lithographically imprinted on the substrate along with themicroelectrodes. Other common electrical elements can be included, suchas electrically conducting traces, rectifiers (e.g., diodes), resistors,capacitors, power conditioning elements, transistors (e.g., MOSFETs),and any of the other elements used in integrated circuits, such asmicroprocessors and other elements used in SSI, MSI, VLSI, and ULSIintegrated circuit technologies. In some embodiments, the electricallyconducting traces or other wiring are made of a superconductingmaterial.

In one set of embodiments, power is provided to each of themicroelectrodes by direct electrical connection (i.e., wiring) betweenthe power source and microelectrodes. The direct electrical poweringmeans includes features for controlling electrical powercharacteristics, such as any of the current and voltage characteristicsknown in the art. In some embodiments, all of the microelectrodes arecollectively powered and adjusted, i.e., the microelectrodes are notindependently powered and adjusted, and thus, not independentlyaddressable. In other embodiments, each of the microelectrodes isindependently addressable, i.e., each microelectrode can beindependently powered or turned off, and each powered microelectrode canbe independently electrically adjusted.

In another set of embodiments, the microelectrodes are wirelesslypowered. Any of the wireless technologies known in the art areapplicable herein, as appropriately modified to suit the particularrequirements of the instant invention. For example, the microelectrodescan be configured to be in electrical communication with a receivingcoil, wherein the receiving coil includes means (i.e., features) thatallow it to produce appropriately conditioned electrical power from awireless transmission source (e.g., a transmitting coil). As known inthe art, the transmission source is generally required to be within anoptimal size, distance and orientation to the receiving coil in orderfor efficient wireless transmission to occur. In some embodiments, thewireless transmission source is a coil that can inductively couple to areceiving coil to produce a current in the receiving coil. In otherembodiments, the wireless transmission source produces a form ofelectromagnetic radiation, such as provided by a radio or microwavesource. The source of electromagnetic radiation can be converted to anelectrical current by a suitable rectifying antenna (i.e., rectenna)capable of converting electromagnetic energy into electrical energy. Inother embodiments, a receiving coil and rectenna are both used. Inparticular embodiments, each microelectrode or group of microelectrodesis provided with its own independent means for being wirelessly powered.Any of the wireless features described above can be incorporated intothe substrate, along with microelectrodes, by any of the lithographic orphotolithographic means known in the art, such as those described above.Generally, the wireless powering mechanism is used solely for poweringof the microelectrodes while not having a direct effect on theelectrolysis of water, i.e., electromagnetic radiation used in theinstant process for energy transfer or communication is preferably notalso inducing the splitting of water by photolysis. In particularembodiments, photolysis means are excluded from the instant electrolyticapparatus and/or process. In related embodiments, a radiofrequencyplasma source is excluded from the instant electrolytic apparatus and/orprocess.

In other embodiments, the electrical powering means can further includefeatures for monitoring the performance of each microelectrode. Forexample, by incorporation of appropriate electrical detection devicesknown in the art, voltage and current levels of each microelectrode canbe monitored and appropriately adjusted. Integrated computer chips canalso be incorporated into the microelectrode design in order toregularly monitor and/or adjust the electrical power of eachmicroelectrode. In some embodiments, the computer chips are programmedby an appropriate algorithm to keep each of the microelectrodes withincertain current and/or voltage limits during performance. The computerchips may also detect malfunctioning or non-optimal performance of amicroelectrode and transmit this information to an external source, suchas a computer, for further evaluation by a process control operator.

In another set of embodiments, the microscaled electrodes, describedabove, are not included, but the same or similar benefits of microscaledelectrodes are instead provided by modifying a bulk metal electrode toinclude on its surface a plurality (i.e., distribution) of microsized ornanosized high energy points (i.e., catalytic hot spots). In theforegoing embodiment, the distribution of catalytic hot spotsfunctionally mimics a patterned array of microelectrodes. In particularembodiments, random catalytic hot spots are built into a bulk electrodeby appropriate adjustment of catalyst grain size and domain structuresduring manufacture of the catalyst. In other methods, a distribution(either ordered or random) of protrusions are built into the bulkcatalyst by, for example, a physical or chemical etching process, or bya physical and/or chemical additive process (e.g., by a PVD or CVDprocess). Some of the possible specific means for introducing thesefeatures in a bulk catalyst are provided by techniques discussed in, forexample, B. Glowacki, et al., Materials World, vol. 6, no. 11, pp.683-686 (November 1998), the contents of which are incorporated hereinby reference in their entirety. In some embodiments, the techniques ofmetallography and crystallography are used to characterize themicrostructures of the electrode materials as a guide for the nextiteration in the preparation on an improved electrode. To determine if asuitable or desired distribution of catalytic hot spots has beenachieved on the electrode, the electrode material can be tested forelectrolytic bubble distribution on the surface of the electrode.

Catalytic hot spots can be defined as the points of oxygen or hydrogenbubble formation on a bulk metal electrode. It is known in the art thatthe surface area occupied by the hot spots is a small percentage of thegeometric area of the bulk electrode (e.g., E. Greenbaum, et al.“Metabolic Prosthesis for Oxygenation of Ischemic Tissue,” IEEE Trans.Biomed. Engin., 56, 528-531 (2009)). It is also known in the art thatelectronic conduction in polycrystalline materials depends on the size,structure and distribution of the grain boundaries of the crystallites(e.g., Springer Handbook of Electronic and Photonic Materials by SafaKasap and Peter Capper (2006)). Materials and their grain boundarycharacteristics can be designed with improved electronic performance andin some cases smart capabilities to provide more reliable electronicdevices and systems with improved functionality. For example, in amaterial containing grain boundaries, charge carriers are generallyscattered at the interfaces between grains. By careful design of grainboundaries, this scattering can be made useful. Obstructing or divertingthe flow of electrons by grain design allows the control ofmicroelectronic pathways in the bulk material leading to, for example, astatistically uniform distribution per unit area of catalytic hot spotson the surface of the bulk electrodes. This distribution canfunctionally mimic a patterned array of microelectrodes.

At least one possible advantage of using such a modified bulk electrodein lieu of an array of microelectrodes is the ability to dispense withthe wiring or wireless communication typically employed in managing anarray of microelectrodes. Furthermore, the same advantages provided byan array of microelectrodes (i.e., dispensing of an ion-permeablebarrier) is also applicable in this embodiment.

Still other modifications are possible for replacing an array ofmicroscaled electrodes with a functional mimic of an array ofmicroscaled electrodes. For example, in another embodiment, thefunctional mimic of the array of microelectrodes can be provided bymodifying a bulk catalytic electrode to contain on its surface a coating(e.g., a hermetic insulating layer) that contains a distribution ofmicroscaled openings therein, thereby permitting the bulk catalyst tomake contact with the electrolyte only at the openings in the coating.The porous coating can be adhered to the bulk catalyst by any suitablemethod. For example, a suitable insulating porous (i.e., macroporous,microporous, mesoporous, or nanoporous) film can be affixed to thesurface of the bulk catalyst, or a portion thereof, by methods known inthe art (e.g., by a heat bonding or lamination process). Alternatively,an insulating coating may be applied to the surface of the catalyst bymeans well known in the art, and this followed by a hole patterningprocess by means known in the art. In the foregoing embodiment, thedistribution of microscaled openings functionally mimics a patternedarray of microelectrodes. Again, at least one possible advantage ofusing such a modified bulk electrode in lieu of an array ofmicroelectrodes is the ability to dispense with the wiring or wirelesscommunication employed in managing an array of microelectrodes. As withthe previous embodiment, the same advantages provided by an array ofmicroelectrodes (i.e., dispensing of an ion-permeable barrier) is alsoapplicable in this embodiment.

In some embodiments, the above two embodiments which employ a functionalmimic of microelectrodes do not include microelectrodes for anyelectrode, i.e., for electrode and counter-electrode. In otherembodiments, at least one electrode is configured as a functional mimicelectrode, described above, while one or more other electrodes (forexample, one or more counter electrodes) contain an array ofmicroelectrodes, according to any of the embodiments described above. Inyet other embodiments, at least one electrode is configured as afunctional mimic electrode, described above, while one or more otherelectrodes are bulk electrodes of the art.

The electrolysis apparatuses described above also include a containerfor holding an aqueous electrolyte and housing the anode and cathode.The container may be an integral, separate, or detachable component ofthe electrolytic apparatus. In embodiments where a partition separatesthe anode and cathode, as described above, the partition may be anintegral (i.e., permanent and non-removable) or detachable element ofthe container. In embodiments where at least one of the electrodes iscomprised of a substrate containing microelectrodes embedded thereon,the substrate can function as an integral or detachable element of thecontainer. The means for collecting evolved gases may also be anintegral or detachable element of the container.

In addition to the above-described features of the electrolysisapparatus, the apparatus typically includes means for the entry and exitof the aqueous electrolyte, particularly for the purpose of replenishingthe aqueous electrolyte. In some embodiments, one or morefluid-transporting conduits (e.g., hoses or pipes) integrally ordetachably connected to the container are included in the apparatus. Insome embodiments, the container includes at least one built-in inlet andat least one built-in outlet for this purpose.

In other aspects, the invention is directed to a method of producinghydrogen and oxygen gases by operating any of the electrolysisapparatuses described above. In the method, an electrolyzer, asdescribed above, is charged with an aqueous electrolyte, and theelectrolyzer electrically powered to produce hydrogen and oxygen gasesby the electrolytic splitting of water. In some embodiments, the aqueouselectrolyte is pure water, i.e., water in the substantial absence ofionic species, or with trace amounts of an ionic species, as would beobtained by purifying water via filtration, reverse osmosis, and/ordistillation. A trace amount of ionic species is typically an amount inwhich the water remains relatively non-conductive (e.g., up to or lessthan 0.1, 0.01, or 0.001 S/m), which may correspond to a saltconcentration of or less than, for example, 0.1, 0.05, 0.01, 0.001, or0.0001 mM of the ionic species. In other embodiments, the aqueouselectrolyte includes a sufficient amount of ionic species to make thewater appreciably conductive, e.g., a conductivity of over 0.1 S/m, orat least 0.2, 0.5, 1, 1.5, 2, 2.5, 3, 3.5, 4, 5, 10, 50, or 100 S/m.

In some embodiments, the ionic species is a salt. The salt can beessentially any salt that is soluble in water, and preferably,completely soluble (e.g., up to 5, 10, 20, 50, or 100 g/L), in water. Insome embodiments, the salt is non-metallic, such as an ammoniumhydroxide or ammonium halide salt. The non-metallic salt can also beorganic (e.g., tetramethylammonium hydroxide). In other embodiments, thesalt is a metal salt, such as a metal hydroxide, metal halide (e.g.,metal fluoride, chloride, bromide, or iodide), metal nitrate, metalchlorate, metal perchlorate, or metal acetate. Some examples of metalsthat can be included in the metal salt include the alkali metals (e.g.,Li, Na, K), alkaline earth metals (e.g., Mg, Ca, Sr), non-reactivetransition metals (e.g., Mn, Fe, Co, Zn), and non-reactive main groupmetals (e.g., Al, Ga). In some embodiments, one or more of any of theabove classes or specific types of ionic species are excluded from theaqueous electrolyte.

In some embodiments, the ionic species is basic, such as any of thehydroxide salts described above. In other embodiments, the ionic speciesis acidic. Some examples of acidic ionic species include any of theorganic and inorganic acids known in the art, such as acetic acid,hydrochloric acid, nitric acid, sulfuric acid. In other embodiments, theionic species can include a superacid, such as trifluoromethylsulfonicacid or a bis-(perfluoroalkylsulfonyl)imide acid, or an organic or metalsalt thereof. The ionic species can also be any of the non-reactiveionic polymers or ionic liquids known in the art. In some embodiments,one or more of any of the above classes or specific types of ionicspecies are excluded from the aqueous electrolyte.

In some embodiments, the aqueous electrolyte includes only water as asolvent. In other embodiments, the aqueous electrolyte includes one ormore water-soluble solvents. Some examples of water-soluble solventsinclude the alcohols (e.g., methanol, ethanol, isopropanol, or ethyleneglycol), acetonitrile, ethers (e.g., dimethoxyethane), andpolyalkyleneoxides (e.g., polyethyleneglycols). The solvent can serve,for example, as a surfactant to improve the efficiency of the process.If used for its surface wetting properties, the solvent can be includedin an amount of up to, for example, 10, 5, 1, 0.5, or 0.1% by weight orvolume of the electrolyte.

In some embodiments, the electrolyzer is powered by a conventional(i.e., non-renewable) power source, such as electricity emanating from aconventional power plant or battery, wherein the battery may berechargeable. In other embodiments, the electrolyzer is electricallypowered by a renewable power source. Some examples of renewableelectrical power sources include solar energy (i.e., electricityproduced from a solar cell), hydroelectric, wind, and geothermal energy.In other embodiments, the electrolyzer is powered by a process in whichexcess or byproduct thermal energy is produced. The process producing anexcess or byproduct amount of thermal energy can be, for example, anindustrial manufacturing process or a nuclear power plant.

In some embodiments, any of the electrolytic methods described above forproducing hydrogen and/or oxygen is coupled to one or more processesthat utilize hydrogen and/or oxygen gas. By being coupled to one or moreprocesses that utilize hydrogen and/or oxygen gas, the electrolyticapparatus can be physically connected to one or more process operationswhere hydrogen and/or oxygen is utilized such that hydrogen and/oroxygen gas is transported directly from the electrolyzer into the one ormore process operations. Alternatively, the electrolytic method can becoupled to one or more processes although the electrolytic apparatus isnot physically connected to one or more of the process operations. Forexample, hydrogen and/or oxygen produced by the electrolytic apparatuscan be collected in a container and transported to one or more processoperations to be used therein.

In a first set of embodiments, the electrolytic method described aboveis coupled to a Fischer-Tropsch (FT) process for the synthesis of liquidhydrocarbons (generally, of the formula C_(n)H_(2n+2)). As known in theart, the Fischer-Tropsch process can be conveniently described by thefollowing set of reactions:

(2n+1)H₂+nCO→C_(n)H_(2n+)nH₂O

The numerous conditions typically employed in the FT process (e.g.,catalysts, temperatures, and pressures) are well-known in the art.According to methods of the art, hydrogen for the FT process istypically provided by gasification of a carbonaceous feedstock, mostcommonly coal gasification (i.e., 3C+H₂O+O₂→H₂+3CO). Since the H₂/COmolar ratio generally produced by coal gasification processes is about0.7, as compared to the ideal H₂/CO molar ratio of 2 for FT processes,the H₂/CO molar ratio produced by coal gasification processes istypically further adjusted by the water-gas shift reaction (i.e.,CO+H₂O→CO₂+H₂). However, the water-gas shift reaction is an energyintensive process requiring high temperatures and the use of copiousamounts of metal catalyst. Therefore, at least one advantage in couplingthe instant electrolysis process with the FT process is that hydrogenproduced from the instant electrolysis process can be mixed into asyngas feedstock mixture produced by coal or biomass gasification toincrease the H₂/CO ratio while not relying on a water-gas shift reactionfor this purpose.

In a second set of embodiments, the electrolytic method described aboveis coupled to a petroleum refining process. Of particular focusaccording to the instant invention are those petroleum refiningoperations that require hydrogen gas. Some examples of such petroleumrefining operations include hydrodealkylation, hydrodesulfurization, andhydrocracking operations. The numerous conditions typically employed inthe foregoing petroleum refining operations (e.g., catalysts,temperatures, and pressures) are well-known in the art.

In a third set of embodiments, the electrolytic method described aboveis coupled to a Haber process for the production of ammonia. As known inthe art, the Haber process can be conveniently described by thefollowing overall reaction:

N₂+3H₂→2NH₃

The numerous conditions typically employed in the Haber process (e.g.,catalysts, temperatures, and pressures) are well-known in the art. TheHaber process is relied upon for producing millions of tons offertilizer per year. Thus, millions of tons of hydrogen gas are neededto sustain the Haber process. Currently, hydrogen gas used in the Haberprocess is provided by gasification and steam reforming of fossil fuels.Since fossil fuels are non- renewable, and gasification and steamreforming of fossil fuels are environmentally detrimental and costly,the instant embodiment is quite beneficial by providing large quantitiesof hydrogen gas from a renewable source (i.e., water) and withoutrelying on fossil fuels in sustaining the Haber process.

In a fourth set of embodiments, the electrolytic method described aboveis coupled to a hydrogenation process. The hydrogenation process can beany process that uses hydrogen gas. For example, the hydrogenationprocess can be a coal liquefaction process for the production of liquidhydrocarbons. As known in the art, the coal liquefaction process can beconveniently described by the following overall set of reactions:

nC+(n+1)₂→C_(n)H_(2n+2)

The numerous conditions typically employed in the coal liquefactionprocess (e.g., catalysts, temperatures, and pressures) are well-known inthe art, e.g., the Bergius process. Other hydrogenation processeswell-known in the art include the hydrogenation of unsaturatedcompounds, as found in the conversion of maleic acid to succinic acid,and the conversion of unsaturated fats to saturated fats.

Several other processes can make use of the hydrogen gas produced by theelectrolytic process described above. For example, current large-scalemethanol production generally relies on the reaction between carbondioxide and hydrogen, wherein the hydrogen is conventionally obtained bysteam reforming of methane. Hydrogen chloride (HCl) production alsorequires large amounts of hydrogen (i.e., by reaction of hydrogen andchlorine gases). Thus, both of these processes would also benefit by theinstant hydrogen production process.

A particular process that may benefit in utilizing oxygen produced bythe electrolytic process described above is the smelting of iron oreinto steel. Other processes that may benefit include metal cutting andwelding processes and equipment, as well as water treatment processes.

In other aspects, the invention is directed to a method for producingspecies other than hydrogen or oxygen using the electrolytic apparatusdescribed above. Species other than hydrogen and oxygen can be obtainedby suitable selection and adjustment of the aqueous electrolyte, as wellas appropriate adjustment of the operational characteristics of themicroelectrodes (e.g., current, voltage, and catalytic characteristics).

In a particular set of embodiments, the electrolytic method describedabove is modified to function as a chloralkali process. As known in theart, the chloralkali process occurs by the electrolysis of an aqueoussolution of a metal chloride, M^(+y)Cl_(y), where y is at least 1 and upto 6, but more typically 1 or 2. At the anode, chlorine (Cl₂) isproduced by the oxidation of chloride anion (along with minor productionof oxygen gas), i.e., according to the half-reaction: 2Cl⁻→Cl₂+2 e⁻. Atthe cathode, hydroxide ion is produced by the reduction of water tohydrogen according to the following half-reaction: 2 H₂O+2e⁻→H₂+2 OH⁻.Metal ions (i.e., M^(+y)) migrate from the anode to the cathode to formmetal hydroxide species (i.e., M^(+y)(OH)_(y), where y is as definedabove). Generally, the metal ion (i.e., M^(+y)) considered herein is ahard metal ion with a low propensity for being reduced. Thus, theoverall reaction may be conveniently expressed as follows:M^(+y)Cl_(y)+y H₂O→y/2 Cl₂+y/2 H₂+M(OH)_(y).

Some particular types of metal ions (i.e., M^(+y)) considered hereininclude the alkali metals (e.g., Li⁺, Na⁺, K⁺), alkaline earth metals(e.g., Mg⁺², Ca⁺², and Sr⁺²), as well as transition and main groupmetals that are resistant to reduction (e.g., Zn⁺² and Sn⁺²). Inparticular embodiments, the metal chloride is sodium chloride, and thus,the metal hydroxide produced at the cathode is sodium hydroxide, asshown in the following overall equation:

2NaCl+2H₂O→Cl₂+H₂+2NaOH

Typically, an ion-permeable or ion-conducting membrane is used in thechloralkali process to prevent mixing of chlorine and hydroxide sincethese species are reactive with each other to produce, for example,hypochlorite (ClO⁻) and chlorate (ClO₃ ⁻) species. The ion-permeable orion-conducting membrane will selectively allow only positive ions (e.g.,metal ions and protons) to pass into the cathode compartment. However,in embodiments where hypochlorite or chlorate is desired as anendproduct, a membrane may not be used, or a partition that permitsmixing (as described above) is used. As known in the art, the relativeamount of chlorine compared to chlorine oxide species is also dependenton the pH and operating temperature. For example, it is known that,while chlorine is generally the predominant component at low pH (i.e.,less than 7), hypochlorous acid (HClO) is generally the predominantcomponent at neutral pH (i.e., about 7), and hypochlorous acid ion(ClO−) is generally the predominant component at high pH (i.e., above 7,and more generally, at or above 9). Furthermore, elevated temperaturesare known to favor the formation of chlorate over hypochlorite whenmixing is permitted. Other numerous conditions typically employed in thechloralkali process (e.g., electrode compositions, metal-halideconcentrations, and the like) are well-known in the art. For example, itis well known that, due to the corrosive nature of chlorine produced atthe anode, the anode should be made of a material unreactive withchlorine, such as any of the non-reactive electrode materials describedabove, and in particular, titanium or titanium alloys with othercatalytic electrode materials. Moreover, it is generally known that aparticularly suitable cathode material for the chloralkali process isnickel or a nickel alloy. In particular embodiments, the chloralkaliprocess described above is electrically powered by a renewable energysource or a source producing excess or byproduct heat, as describedabove.

In yet another aspect, the invention is directed to a process in whichthe above-described chloralkali process is coupled to a process thatuses chlorine gas or a metal hydroxide produced by the chloralkaliprocess. Some examples of processes that use chlorine gas include avariety of industrial processes for producing chlorinated chemicals(e.g., solvents, insecticides, and plastics). Some examples of processesthat use metal hydroxides, and sodium hydroxide in particular, includeprocesses for producing lye formulations, paper, alumina, detergents,and a variety of organic salt compounds (e.g., carboxylate salts).Sodium hydroxide, in particular, is also used in oil drilling (e.g., asa component in drilling mud) and fuel manufacturing operations (e.g., toremove sulfurous contaminants).

FIG. 1 a is an embodiment of a two-compartment modular structure for theelectrolytic production and separation of hydrogen and oxygen. Element 2is the hydrogen production compartment. Element 4 is the oxygenproduction compartment. Element 6 is a common wall that separates thetwo compartments. Element 8 is a wafer electrode assembly embedded inthe common wall 6. Element 10 is a primary transmission coil that powers8 via Faraday's law of electromagnetic induction. Separate streams ofhydrogen and oxygen are collected via the exit ports at the top of theirrespective collection towers.

As illustrated in FIG. 1 a, in particular embodiments, silicon planarwafers are included in a membrane barrier to produce H₂ and O₂ inseparate compartments. Photolithography is used to lay down the patternof bond pads, electric current-carrying traces and electrodes. A polymeror metal oxide coating provides an electrically insulating barrierbetween the wafer, electrical traces, and the water. The insulatingcoating is removed from the face of the electrodes to expose only theportions that are needed to contact the water for the electrolyticreactions. Electrodes on the wafers may be powered by direct bond padconnections, or as depicted in FIG. 1 a, wirelessly via inductivelycoupled power transmission.

As also shown in FIG. 1 a, H₂ and O₂ collection towers are sized tominimize pressure differences between their respective collectioncompartments. The towers may be operated above atmospheric pressureaccording to principles embodied in the Nernst equation. If powered byinductive coupling, the H₂ and O₂ collection towers are self-contained,free-standing units located in close proximity to the transmittingcoils.

FIG. 1 b is a detailed view of the wafer electrode assembly 8 shown inFIG. 1. Elements 12 are patterned cathodes on the first surface of thewafer. Elements 14 are corresponding patterned anodes on the secondsurface. Through vias, perpendicular to the surface, connect eachcathode-anode pair to a voltage source that powers the electrolysis ofwater. Elements 16 are pores (holes) that allow the movement of ionsbetween the two sides of the wafer. In particular, 16 facilitatesmaintenance of electroneutrality on both sides of the wafer aselectrolysis proceeds. Element 18 is the secondary receiving coil thatreceives power from the primary transmitting coil 10 (as indicated inFIG. 1 a). For clarity, 18 is shown in an “exploded” view above thesurface of the wafer. In practice, 18 is on or close to the surface ofthe wafer. Secondary receiving coil 18 may be fabricated as part of thelithography process, or it may be a separately prepared coil that isadded to the wafer. Element 20 is the power-conditioning block thatgenerates the DC voltage for electrolysis. In addition to wirelesspower, bidirectional information wireless telemetry 22 is used tomonitor and control the operating conditions of the wafer such as thecurrent and voltage parameters of each electrode. Element 24 is an insetto FIG. 1 b as further shown in FIG. 2, and as discussed below.

FIG. 2 is an inset to FIG. 1 b providing a detailed view of hydrogenproduction at cathode 12, oxygen production at corresponding anode 14,and maintenance of electroneutrality on both sides of the wafer via themigration of hydrogen ions through pore 16. As illustrated in FIG. 2, inparticular embodiments, electroneutrality between the H₂ and O₂collection compartments is maintained by proton-conducting micro- ornano-channels in close proximity to the patterned electrodes. Element 26is a voltage means for powering the electrolysis of water.

FIG. 3 illustrates an exemplary set of process steps that can be usedfor wafer preparation. In the exemplary process, silicon wafers (e.g.,two-inch diameter, 50 μm thick) can be used as substrates. The wafersare preferably characterized using a variety of imaging and microscopytechniques including atomic and Kelvin force microscopies. If desired orfound necessary, protective polymer coatings, such as parylene, can beapplied.

To fabricate the through vias or pores, standard nanofabricationprocesses can be used. FIG. 3 demonstrates a particular fabricationprocess. As shown in FIG. 3, first, the thin silicon substrate (˜50microns), as shown in Step 1 of FIG. 3, is lithographically patterned toproduce structure of Step 2 in FIG. 3. Through vias can be reactive-ionetched using a deep silicon reactive ion etch system capable of theso-called Bosch etch process as well as cryogenic etching. Next, theetched substrate is oxidized, preferably in an O₂ or H₂O atmosphere, tocreate a thin insulating barrier as shown in structure of Step 3 in FIG.3. Finally, as shown in structure Step 4 in FIG. 3, electrodes can bedeposited via physical vapor deposition (evaporation or sputtering)using an off-axis orientation to shadow the through vias. The electrodescan be subsequently patterned using a lift off process or standardlithography/etch process (not shown).

For rising bubbles under laminar flow conditions, the cross migration ofH₂ and O₂ is typically negligible. For example, if the height of thecollection tower in FIG. 1 a is 10 meters, the maximum escape time forthe bubbles can be calculated as 40 seconds. On the other hand, for anaqueous path length of 1 mm, the characteristic diffusion time foroxygen is 254 seconds. Moreover, oxygen is not especially soluble inwater, i.e., 284 μM at 20° C. and 1 atm. It is even less soluble inelectrolytes because of the well-known “salting-out” effect. See, forexample, Davis et al, “Solubility and Diffusion Coefficients of Oxygenin Potassium Hydroxide Solutions”, Electrochimica Acta, 12, 287-297(1967), the contents of which are herein incorporated by reference intheir entirety. Experiments can be performed to measure the degree ofcross-migration and the onset of turbulence. For example, working withwafers produced in Step 3 of FIG. 3, experiments can be performed withpores (e.g., of 1, 3, 10, 30, 100 and 500 μm diameters) in conjunctionwith the test assembly shown in FIGS. 4 a and 4 b, which illustrate thewafer, pores, and opposing 100 μm diameter wire electrodes withadjustable distances from the surfaces of the wafer.

Visual inspection has shown that bubble formation can be divided into atleast two phases. At low currents (e.g., <1 mA), the bubbles grow at theelectrode surface, break free and ascend in a quiescent laminar stream.However, at significantly higher currents (e.g., >1 A), the bubbles tendto burst forth violently, causing turbulence and cross-contamination ofthe product streams. Increasing the size of a single electrode does notalleviate the problem because the gases are produced at catalytic “hotspots,” and not uniformly across the surface as a geometricrepresentation of the electrode would suggest. In some embodiments, thecurrent provided to each microelectrode is kept below a thresholdcurrent in order to prevent or minimize turbulence that could causecross contamination. For example, in different embodiments, depending onseveral factors including the size and design of the microelectrodes,the threshold current can be at or below, for example, 1 A, 500 mA, 250mA, 100 mA, 50 mA, 25 mA, 10 mA, 5 mA, 1 mA, 0.5 mA, 0.25 mA, or 0.1 mA,or within a range bounded by any two of the foregoing values.

If desired or found necessary to further ensure the prevention ofcross-contamination, the pores can be modified with a proton-conductingpolymer. The use of a proton-conducting polymer can also permit anincreased threshold current for cross-migration of O₂, or even allowoperation without limitation by a threshold current altogether. Porescan be modified with a proton-conducting polymer by methods known in theart. For example, precursor chemicals, such as bifunctional silanes (ascommercially available from, for example, Gelest, Inc.) can be used toattach a proton-conducting polymer to a semiconducting substratesurface. In some embodiments, the bifunctional silanes contain or aremodified to contain proton-exchange groups. Bifunctional silanescontaining proton-exchange groups can be the same bifunctional silanesused in preparing silica-based ion-exchange resins, which are used in,for example, chromatography and water purification.

In a first set of embodiments, the pore modification process includesdirect coating of a porous silicon or silica material (or other oxide orsemiconductor material) with a bifunctional silane containing or furthermodified to contain proton-exchange groups on a free end, i.e., the endnot bound to the substrate (see, for example, Arkles, B. (1977)Tailoring Surfaces with Silanes, Chemtech, 7, pp. 766-778, the contentsof which are incorporated herein by reference in their entirety). In asecond set of embodiments, the pore modification process includesfilling pores with proton-conductive “brush” copolymers that areattached to the silicon surface with bifunctional silanes (see, forexample, Yameen, B., et al., (2008) J. Am. Chem. Soc., 130, pp.13140-13144). In a third set of embodiments, the pore modificationprocess includes filling membrane pores with porous xerogels containingproton-exchange functionalities imparted by grafting or encapsulation,such as by infusion of silica sol gels and proton-exchange polymers intothe pores (see, for example, Gautier, C., et al. (2006) Langmuir, 22,pp. 9092-9095, and Pichonat, T., et al. (2006) Microsyst. Technol., 12,pp. 330-334, the contents of which are incorporated herein by referencein their entirety). Synthesis of such silica-sol-based xerogels is maderelatively straightforward by the availability of inexpensive,commercially available precursors and their ease of preparation.

A wide range of materials can be incorporated using any of theapproaches described above (see, for example, Laughlin, J. B., et al.(2000) J. Chem. Educ., 77, pp. 77-79, the contents of which areincorporated herein by reference in their entirety). The brush-copolymermethod, in particular, increases potential proton-exchange capacity andselectivity by increasing the number of proton-exchange groups persilicon surface area of the pores. In particular embodiments, the poremodification process can include the encapsulation of Nafion 117 orother proton-exchange polymer in porous (e.g., mesoporous) silica by solgel condensation of tetramethylorthosilicate.

In accordance with a particular aspect of the invention, modern methodsof integrated circuit technology are used to produce an electrolyticsystem having wireless power and information transfer. The productionand operation of electronic circuitry in aqueous environments is wellknown in the art. See, for example, D. Zhou and E. Greenbaum (Eds.),Implantable Neural Prostheses, Vol. 1 (2009) and Vol. 2 (2010),Springer, New York. An electrolytic system particularly underconsideration herein contains a planar electroactive structure thatcontains one or more electrolytic electrode pairs, a coil for receivingpower and information, power conditioning circuits, and electroniccircuitry for bidirectional information transfer between theelectroactive electrodes and a process control center for controllingand optimizing the production of hydrogen and oxygen. However, not allof the foregoing features need to be used. For example, there may becertain applications where wireless power or bidirectional telemetry isnot needed.

The planar electroactive structure could be a silicon wafer of anappropriately chosen diameter. A selection of diameters in the range of2-12 inches are commercially available. Integrated circuits on thesilicon wafers are designed to perform the electrolysis of water. Thewafer and its associated electronics are preferably hermetically sealedexcept for appropriate exposure of the electrocatalytic surfaces of theelectrodes on either side of the wafer that will evolve the hydrogen andoxygen. In particular embodiments, the planar structure of the waferforms a barrier that facilitates separation of the hydrogen and oxygenthat are formed on opposite sides of the wafer barrier. Microelectrodescan be embedded on each side of the wafer barrier. In particularembodiments, electrode pairs formed of electrodes on opposite sides ofthe wafer draw separate power from a power source, such as a rectenna.Additional wireless circuitry can be included to collect informationabout the productivity of each electrode pair and to control the currentand voltage levels of each electrode pair.

In some embodiments, the hermetically protected wafer is sealed in thewall of a rectangular tubular structure, whose geometry, with interiorand exterior regions, lends itself to the collection of the hydrogen andoxygen. Multiple silicon wafer units can be sealed in one or more wallsof the tubular structure. Power transmitting coils are appropriatelydesigned and positioned to maximize mutual inductance and power transferbetween the transmitting coils of the power source and the receivingcoils of the wafers. This modular tubular unit, with multiple wafers,can be scaled-up for large-scale hydrogen and oxygen production.

FIG. 6 is a perspective detailed view of the electrolysis of wateraccording to an embodiment of the present invention. FIG. 6 illustratesan embodiment where a silicon wafer electrode assembly 8 is sealed inthe wall 6 of a two compartment gas-collecting rectangular tube (i.e.,“rectangular tube”). In FIG. 6, common wall 6 contains embedded waferelectrode assembly 8. Element 12 is a cathode (or a plurality ofcathodes) on the first side of the wafer. Element 14 is an anode (or aplurality of anodes) on the second side of the wafer. Element 16 is apore (or a plurality of pores) for maintaining electroneutrality. InFIG. 6, pore 16 is illustrated in the common wall. In other embodimentsit is in the wafer. In yet other embodiments, multiple pores are presentin both the wafer and wall. Electrical contact on the opposite side ofthe wafer is preferably achieved using electrical conducting meansperpendicular to the plane of the wafer. One example of such means isthrough silicon via technology which is well known in the art (see, forexample, U.S. Pat. Nos. 7,683,459 and 7,633,165). Element 18 is thesecondary receiving coil that receives power from the primarytransmitting coil (not shown). Element 20 is the power-conditioningblock that generates the DC voltage for electrolysis. Bidirectionalinformation wireless telemetry 22 is used to monitor and control theoperating conditions of the wafer, such as the current and voltageparameters of each electrode.

The silicon wafer shown in FIG. 6 contains cathode and anodemicroelectrodes on opposite sides of the wafer, and the microelectrodesare in electrical communication with a power source that will drive theelectrolysis. The rectangular tube forms enclosures (see FIG. 1 a) thatseparates a first volume where hydrogen can be produced from a secondvolume where oxygen can be produced. Water is on both sides of thecommon wall and is in contact with the electrolytic electrodes. At leastone pore maintains electroneutrality during electrolysis. The powertransmitting coil sends power to a rectenna, which contains thereceiving coil and the power conditioning electronics. Rectennas arewell-known devices that receive power in the form of electromagneticenergy and convert them to usable electrical power. The rectennaschematically illustrated in FIG. 6 is comprised of a receiving coil andpower block that conditions the electrical power for electrolysis. Thisconditioning generally includes rectification and smoothing. Additionalelectronics, not illustrated, may also be present. For example,bidirectional electronic control circuitry can be included to monitor,control, and set the current and/or voltage levels of each electrolyticelectrode pair. This is accomplished with bidirectional telemetrybetween the data of the electrodes and control units that interactwirelessly with each electrode pair that is involved in electrolysis.Although FIG. 6 illustrates only one such pair, many electrolyticelectrodes can be present on the silicon wafer, each with its owncontrol electronics and power. The current and voltage values aregenerally determined by the plant manager in order to suitably adjust oroptimize operation of the system. Current and/or voltage can beincreased or decreased to likewise increase or decrease hydrogen and/oroxygen output, and to stay within electrode operating limits. The waferis preferably hermetically sealed except for the electrode, which refersto the electrocatalyst surface on which the electrolysis of wateroccurs.

It is well known in the art of wireless power transmission that closedistances and proper orientation optimize overall efficiency. Thus, insome embodiments, the interior area of the tubing is occupied by thetransmitting coil which is placed in close proximity to the receivingcoil because this will maximize power transfer.

Multiple silicon wafers can be sealed in the wall. If the cathodes arefacing a first compartment of the tubing, hydrogen will be collected inthat compartment. Hydrogen gas can then be captured and used as needed.In some embodiments, several such wafers are embedded, each with amultiplicity of electrodes for performing the electrolysis of watersimultaneously.

FIG. 6 shows one possible way that the silicon wafer can be sealed inthe wall of the rectangular tube. One mode of operation is for hydrogento be produced internally and oxygen to be produced externally of therectangular tube. The wafer is preferably hermetically sealed with anon-conducting polymer except for exposure at the catalytic portion thatelectrolyzes water to hydrogen and oxygen.

FIG. 8 is a simplified illustration of how the hydrogen can becollected. The transmitting coils, wafer, and other elements are omittedfrom the figure for simplicity. Element 42 is the hydrogen compartment.Element 44 is the feed tube to provide replacement for the waterconsumed in the electrolytic process. Hydrogen bubbles rising in thecompartment reach headspace 48. Hydrogen is removed from the headspacevia tube 50 that is part of a network for product collection. Shutoffvalve 52 can be used to isolate the electrolytic tower from thecollection network for quick removal and servicing or replacement. Inorder for hydrogen or other gas to be collected in the tube, the cathode(or anode) faces the interior of the tube so that gas is produced insidethe tube. For example, hydrogen produced in the interior of the tubularstructure can be collected by capping the top, collecting it, andsending to a compressor for storage or distribution. Water (i.e.,aqueous electrolyte) is generally on both sides of the tube. The oxygenmay also be collected, or alternatively, vented to the atmosphere. Theshut-off valve can be used to disconnect the unit from the pipingnetwork for quick maintenance or replacement.

In some embodiments, the tubular structures are multiple free standingunits that are packed relatively closely to minimize floor space. Such apacking arrangement can help to optimize hydrogen and oxygen output perunit area. Depending on the output of produced gas and other variables,the tubular structures can be columns of average to massive lengths anddiameters (e.g., up to 5, 10, 20, 30, 40, 50, or 100 feet). The tops ofthe tubular units generally transition into a piping system that enablescapture of hydrogen and/or oxygen. If hydrogen is produced in theinterior of the tube, gas capture becomes relatively easy. If desired,both hydrogen and oxygen can be captured by modifying the collection andpiping system.

FIG. 9 illustrates one possible arrangement for transmitting andreceiving coils where the planes of the receiving and transmitting coilsare parallel and close to each other with collinear axes. Only the coilsare shown. In FIG. 9, element 18 is the secondary receiving coil thatreceives power from the primary transmitting coil 10. Element 20 is thepower-conditioning block that generates the DC voltage for electrolysis.In addition to wireless power, bidirectional information wirelesstelemetry 22 is used to monitor and control the operating conditions ofthe wafer such as the current and voltage parameters of each electrode.54 is electromagnetic energy that is transferred from the primarytransmitting coil to the secondary receiving coil. Coils 10 and 18 arepositioned and oriented to maximize energy transfer.

The geometry shown in FIG. 9 is advantageous for maximizing powertransfer. This arrangement is particularly useful if the design of thewafer-rectenna system has the receiving coil parallel to the wafer sinceit maximizes the flux linkages between the two coils.

The invention can be further appreciated by a further detaileddiscussion of its component elements. For example, in particularembodiments, a silicon wafer with an appropriate diameter is chosen. Inone embodiment of the invention, the wafer is powered inductively by itsreceiving coil that is located in close proximity to the transmissioncoil. The receiving coil can be made as part of the integrated circuitprocess or it can be a coil that is manufactured separately and affixedto the wafer. Faraday's Law of Electromagnetic Induction teaches thatmaximum power is transferred to the device when the time rate of changeof magnetic flux linkage through the receiving coil is maximized.Distance and orientation between the coils are important parameters thatenter into the value of mutual inductance. Two convenient orientationssuggest themselves. If the receiving coil is fabricated so that it iseither in or closely parallel to the plane of the silicon wafer, then acorresponding location for the transmitting coil would be one that is inclose proximity to the receiving coil, concentric and parallel to it.Alternatively, the receiving coil may be oriented perpendicular to theplane of the wafer that is sealed in the wall of the cylindrical tubing.Correspondingly, the axis of the receiving coil is collinear with thecentral axis of the tubing. A favorable geometry for this configurationis for the axis of the transmitting coil to be collinear with the otheraxes and placed inside the receiving coil.

For large-scale hydrogen and oxygen production, power delivery bywireless telemetry has practical advantages for service and maintenance.The tubular towers will contain many embedded silicon wafers with eachwafer containing many electroactive electrodes for the electrolysis ofwater. Each of these towers can be freestanding units that are notmechanically connected by wires to any source of power. In someembodiments, the only mechanical connection is the hydrogen collectiondevice at the top of the tower. Using a shut-off valve and quickconnect/disconnect fasteners, these towers can be removed from thesystem for maintenance and inspection without serious compromise of theoverall production output.

Information on productivity, maintenance, and repair for each of themicroelectrodes can be obtained via bidirectional wireless telemetry.The electronic circuitry on the silicon chip directs power to theplurality of electrolytic electrodes that are contained on the wafer.Since a particular embodiment of the process is to produce hydrogen andoxygen on opposite sides of the wafer, the fabrication process caninclude cathode and anode microelectrodes on opposite sides of thewafer. Ideally, each electrode or group of electrodes will have its ownlocal power and electronic control system that measures the currentthrough each electrode and the supply voltage that is used to drive thecurrent. Information on these parameters can be sent wirelessly to acentral computer that is programmed to monitor and control all of themicroelectrodes in the system.

Zero current flowing in an electrode indicates failure for thatelectrode, but not for the system as a whole. Indeed, the productivityof any single electrode is preferably a small fraction of the totalproduct yield. “Fault” is defined as the operational failure of a systemcomponent. “Defect” is defined as failure that is caused by substandardmanufacturing. The system is, therefore, fault tolerant because totaloutput is not seriously affected by the failure of a relatively smallnumber of electrolytic electrodes. It is defect tolerant for certainclasses of manufacturing defects such as small water leakage between thesealed silicon wafer and the tubing because proton conductivity isrequired to maintain electroneutrality during the manufacturing process.

The operation of large-scale hydrogen and oxygen production facilitiesusing this system can be constructed from freestanding two- orthree-compartment modular units. In some embodiments, a single unit iscomprised of a rectangular water-impermeable insulating cylinder intowhich a plurality of electrolytic wafers has been inserted. The cathodesides of the wafers can, for example, face the interior of the cylinder.Hydrogen that is produced in the cylinder's interior can be collected atthe top and sent to a storage or distribution system. Each electrode inthe system preferably can have its own coded address. The status of eachelectrolytic electrode can be continually reported to a computer withdatabase software that monitors the current and voltage state of eachelectrode and its product output. Service and maintenance informationcan also be collected and used to schedule these operations as needed.

FIG. 7 a is an exploded view of an embodiment (i.e., fourth embodiment,as described in the Summary section) in which two separate wafers 8(i.e., first and second rigid planar substrates) sandwich aproton-conducting membrane 68. Elements 16 are pore sections (i.e.,first and second pore sections) that, when the electrolyzer is assembledas shown in FIG. 7 b, align colinearly at the point where they meet onopposite sides of the membrane 68. By being colinearly aligned, thecentral axes of the pore sections are substantially colinear, as shownin FIG. 7 a. The point at which the pore sections 16 meet on oppositesides of the membrane 68 is depicted as the dotted circle shown on themembrane. Each pore section extends from the membrane 68 to at least thefirst planar surface of each wafer 8. Therefore, electrolyte is notallowed to directly transport from one end of the pore to the other, butinstead, is stopped at the membrane which selectively allows passage ofcationic species, such as protons. In some embodiments, the pore islevel with the wafer surface, while in other embodiments, the poreextends a distance from the wafer surface (i.e., as a tubular elementextending from the wafer surface). In some embodiments, each poresection is held tight against the membrane after assembly by beingattached to the wafer and not to the membrane. In other embodiments, oneor both pore sections are attached to the membrane. For a pore sectionthat is attached to the membrane, the wafers can include anappropriately sized gap to fit the pore sections through the waferduring assembly. Generally, each pore section has the same orsubstantially the same internal diameter; however, in some embodiments,the pore sections have different widths, provided that the pore sectionsare substantially overlapping (i.e., substantially colinearly aligned)on opposite sides of the membrane. Although a single partitioned pore isdepicted in FIGS. 7 a and 7 b, two, three, or a greater multiplicity ofsuch pores can be included in the design.

In the foregoing (i.e., fourth) embodiment, the membrane contacts thesecond planar surface of each wafer, while the first planar surface ofeach wafer contains a plurality of microscaled catalytic electrodes.Thus, the first planar surface of each wafer is designed to be incontact with the electrolyte while the second planar surface of eachwafer is designed to be in contact with the membrane. Since the secondplanar surface of each wafer is in contact with the membrane, the secondplanar surface of each wafer generally does not contain microelectrodesor other electronic devices disposed thereon. However, in certainembodiments, the second planar surface of one or both wafers may containelectronic devices or structures, such as any the devices and structures(e.g., bond pads, traces, etc.) described above. While FIGS. 7 a and 7 bdepict a single wafer on each side of the membrane, other embodimentsmay employ multiple wafers on a solid planar substrate material, asdescribed above.

Proton-conducting membrane 68, and/or pores filled with aproton-conducting polymer or gel, prevent bulk fluid flow across theassembly, thereby increasing the level of allowable currents forelectrolysis and improving the purity of the hydrogen and oxygenstreams. An advantage of the embodiment shown in FIGS. 7 a and 7 b isthat this design includes some additional features (particularly thesectional pore) that help to ensure that electrolytic currents remainwithin operable limits of the system. Element 70 is an electricalconducting means running across the wafer electrode membrane assemblythat allows powering electrode pairs on opposite sides of membrane 68.

FIG. 7 b is an assembled view of FIG. 7 a. Pores 16 align colinearly onopposite sides of the proton-conducting membrane 68 that is tightlysandwiched between the wafers. Current-conducting means 70 transmitselectric current across membrane 68. In particular embodiments, one ormore alignment features are included in the assembly package in order toensure proper alignment of hydrolyzer elements, including electroniccomponents and pore sections. The alignment features can include, forexample, markers and/or snap-fit features.

Using any of the electrolytic apparatuses and processes described above,a sufficiently pure gas stream for most applications can be obtained.For example, the produced gas stream may contain a contaminant gas in anamount of or less than 20%, 10%, 5%, 4%, 3%, 2%, 1%, 0.5%, or 0.1%.

For quality assurance purposes, and to monitor the level of gasintermixing or contamination, if any, appropriate testing means can beemployed. An exemplary testing arrangement is provided in FIG. 5. FIG. 5is a view of a test wafer with a single microfabricated electrode thatfurther demonstrates the utility of the present invention. Element 16 isa pore (or multiple pores) that maintains electroneutrality on bothsides of the wafer. Element 36 is a cathode that is exposed to theelectrolytic solution. Element 38 is an electrically conductive tracethat is coated with an insulating layer. Element 40 is an electricalbond pad used to make contact with electrode 36. A corresponding anode,not illustrated, is on the opposite side of the wafer. It has been foundthat hydrogen and oxygen bubbles rising in laminar flow do notappreciably cross-migrate across the wafer, thereby maintaining goodpurity of their respective streams.

In some embodiments, one or more auxiliary means for splitting water,beyond the electrolytic means described above, can be included in theelectrolytic apparatus and/or process. Some examples of these additionalmeans include photolysis (e.g., radiofrequency or microwave), heating,and plasma devices and processes. In other embodiments, one or more suchauxiliary means, or all such auxiliary means, are excluded from theinstant electrolytic apparatus and/or process.

Examples have been set forth below for the purpose of illustration andto describe certain specific embodiments of the invention. However, thescope of this invention is not to be in any way limited by the examplesset forth herein.

Example 1 Microelectrode System on Silicon Wafer Substrate

FIG. 10 is an illustration of a 4″ diameter silicon wafer 8 with 500 μmdiameter etched pores 16 on a 2 mm center-to-center grid. The thicknessof the wafer is 500 μm. Three photolithographed cathodes 36 areillustrated on the near side of the water. Three photolithographedanodes (not visible in FIG. 10) are in mirror positions on the reverseside of the wafer. Electrically conducting traces 38 connect bond pads40 to the cathodes and anodes on either side of the wafer. Bond pads 40are less than a millimeter away from the circumference of the wafer.Traces 38 are coated with an insulating layer. Test clips 56 connect thebond pads to a constant current source In the experiments used to obtainthe test data, the wafer of FIG. 10 is gasket-sealed in atwo-compartment chamber. Electrolyte fills the chamber to a level abovethe pores 16. However, the bond pads 40 are not immersed in theelectrolyte. They protrude beyond the gasket and are in dry air in thelaboratory where electrical contact is easily made. The metal electrodesare exposed to the electrolyte. However, a film of silicon dioxide coatsthe non-electrode portion of the surface and shields it from the 10 mMKOH electrolyte.

Double-side polished 4″ diameter, 500 micron thick, Si (100) n-type(p-doped) wafers were selected that had 1-5 ohm-cm resistivity. Thewafers were thermally oxidized on both sides and the resulting 1.5micron silicon oxide layer subsequently served as both the electricalcontact insulation layer and an etch mask. First, the 1 mm diameterelectrodes along with related conductive paths and contact pads weresymmetrically patterned on both wafer sides using a back-side alignmentoptical lithography and a lift-off process. A variety of metals, such asPt, Ni, Fe, and Co, were e-beam evaporated in vacuum. The metal filmthickness was typically between 100 to 250 nm. A 10 nm thin Cr adhesionlayer was used with Ni, Fe, and Co. For Pt electrodes, a 10 nm Ti layerwas utilized instead. After the lift-off process was completed, thewafers were cleaned in an oxygen plasma and spin-coated with anadditional 7 micron thick layer of photo-resist. A secondphotolithography process was conducted to define an array of 1 mm(and/or 500 micron) diameter pores in the resist. The resist waspost-backed for 90 seconds and the silicon surface was exposed (at thepore locations) to a silicon oxide plasma etch that was followed by aBosch Si etch process that created vias through the entire 500 micronthick wafer. Normally, a thick photo-resist film was sufficient tofinish the etch process. After the wafer was cleaned by hot NMP solventand oxygen plasma, the ALD process was used to passivate both wafersurfaces with a 30 nm thick layer of silicon oxide. The 1 mm diameterelectrodes and contact pads were left uncoated. The ALD technique wasselected to also afford some degree of a protection to the innersidewalls in the pores.

In FIG. 10, the test clips and wires that energize the electrodesapproach the wafer, (oriented vertically) from the bottom. Gaskets onboth sides of the wafer make a hermetic seal between the two glasschambers (FIG. 11) that hold the electrolyte and capture theelectrolytically-produced hydrogen and oxygen.

FIG. 11 is an exploded view of the test apparatus. Electrolysis may beperformed with cathode/anode pairs that are photolithographed on thewafer, as shown in FIG. 10, or with movable wire electrodes 32 and 34that pierce their respective septa, such as 58. Gasket seals 62 oneither side of the wafer are used to seal the wafer electrode assemblybetween two glass enclosures. The wafer becomes the common wall of atwo-compartment chamber. Both compartments are filled with electrolyteto level 64 which is above the pores 16 and the opening in gasket 62.There is no gas-phase diffusion pathway between the chambers. The onlydiffusion pathway between the compartments for dissolved hydrogen andoxygen is in static liquid through the pores. Because the liquid isstatic and the electrolysis currents are chosen to avoid turbulence,there is virtually no convective flow between the chambers. Test leadsfrom a constant current source make contact with the bond pads 40.Insulated traces 38 bring current to electrodes 36. Alternatively,insulated wires with electrolyte-exposed electrodes 32 and 34 used inconjunction with a wafer that has pores 16, but no patterned electrodes(not illustrated), and are positioned at the surfaces of either side ofthe wafer, may also be used. Bubbles of hydrogen and oxygen break freefrom their respective electrodes and rise in the electrolyte to the gasphase headspace 66 in their respective compartments where they escapeand are measured and/or collected via the collection tubes 60. It isknown in the art that the characteristic diffusion times for dissolvedhydrogen and oxygen molecules in static liquid are much longer that thecharacteristic escape times for gas bubbles ascending in static liquidsunder the action of buoyant forces. These principles allow theproduction of separate streams of hydrogen and oxygen with good purity.All pores in FIG. 11 are submerged beneath the liquid level of theelectrolyte. Gas in the headspace provided a diffusion pathway to samplethe gases in the electrolyte headspace that were transported by anitrogen carrier stream to hydrogen and oxygen sensors located on thehydrogen (cathode) side of the cell. The bond pads at the bottom of FIG.11 cleared the gasket allowing for electrical contact with theelectrical power supply as indicated in FIG. 10.

Example 2 Test Run Data for the Microelectrode System

FIG. 12 shows the data for a test run on the microelectrode systemdescribed in Example 1. A 500 μA current was applied to the center pairof electrodes for the wafer of FIG. 10, which is also illustrated in theinset to the figure. The experiment began by sparging the system withhigh-purity nitrogen to eliminate dissolved atmospheric oxygen from theelectrolyte. This provided the initial zero baseline for the hydrogenand oxygen detectors. The nitrogen flow was then turned off, therebyproviding a quiet, static electrolyte in both chambers. Baseline data(at 0 μA) were recorded for about 37 minutes, as shown in FIG. 12. Thecarrier gas that transported H₂ and O₂ to the sensors flowed above theheadspace and did not disturb the quiescent liquid in the chambers.Calibrated hydrogen and oxygen detectors were both located on thehydrogen side of the wafer. The rate of hydrogen production from the 500μA current was observed using a tin-oxide semiconductor sensor for gasphase hydrogen detection that is known in the art. The oxygen detectorwas a Hersch electrogalvanic cell, known in the art for gas phase oxygendetection. This gas-phase O₂ sensor can detect the oxygen productionfrom a 5 μA electrolysis current. The oxygen response in FIG. 12 wasless than 5 μA, thus indicating that the content of oxygen in thehydrogen stream was less than 1%.

Although the presence of oxygen gas in the hydrogen gas stream was <1%,dissolved O₂ is present in the electrolyte. Deliberate introduction ofturbulence in the cell with the nitrogen flow causes easily detectablecross-migration of oxygen into hydrogen compartment.

The experiment of FIG. 13 is similar to FIG. 12 except that 1000 μA wasused. The small response observed for the oxygen data might be baselinenoise or the observation of the onset of turbulence causing a smallamount of cross-migration at this higher electrolysis current. In anyevent the integrated content of oxygen in the hydrogen stream was, as inthe case for 500 μA, less than 1%.

Example 3

Another experiment was performed with a silicon wafer similar to thatdescribed in Example 1 (i.e., FIG. 10). Data for this experiment isshown in FIG. 14. The experiment was conducted similarly to that of FIG.12, except that the wafer electrode assembly of FIGS. 4 a and 4 b (seeinset to FIG. 14) was used in conjunction with the apparatus of FIG. 11.The silicon wafer contained the same pattern of pores, but no patternedelectrodes on the surface. The electrodes in this experiment weremovable platinum wires that were inserted into the cathode and anodechambers via septum ports, as illustrated in FIG. 11. FIGS. 4 a and 4 bdepict a testing protocol for further demonstrating the utility of thepresent invention. Element 28 is a silicon wafer with pores. Aninsulting layer of silicon oxide coats 28. Element 30 is the ensemble ofpores. Element 32 is an insulated wire with an exposed metal cathode.Element 34 is an insulated wire with an exposed metal anode. Cathode andanode abut their respective surfaces on opposite sides of the wafer. Theinsulated platinum wires with exposed metal ends pierced the septum 58,shown in FIG. 11. Each electrode butted the surface of the wafer plane.

FIG. 14 presents the data obtained with the apparatus of FIG. 11 usingwire electrodes 32 and 34. As shown, the content of oxygen in thehydrogen stream was found to be less than 1%. These data validate thebasic physics and chemistry underlying the present invention. They arenot specific to any particular method of electrode fabrication. Thus, asillustrated herein, hydrogen and oxygen bubbles rising in laminar flowdo not appreciably cross-migrate across the wafer, thereby maintaininggood purity of their respective streams.

Example 4

Yet another experiment was performed using no wafer or barrier of anykind in the apparatus of FIG. 11. The electrodes were 1-2 cm apart. Thebubbles rising from each electrode were trapped in separate canopieswhere the hydrogen and oxygen gases were respectively collected andmeasured. The data for this example are presented in FIG. 15 where thecross-migration of oxygen is again <1%. The significance of this resultis that, even in the absence of a physical barrier, for hydrogen andoxygen gases rising in laminar flow streams, very little cross migrationbetween the two gases occurs.

While there have been shown and described what are at present consideredthe preferred embodiments of the invention, those skilled in the art maymake various changes and modifications which remain within the scope ofthe invention defined by the appended claims.

1. An apparatus for the electrolytic splitting of water into hydrogenand/or oxygen, the apparatus comprising: at least onelithographically-patternable substrate having a surface; a plurality ofmicroscaled catalytic electrodes embedded in said surface, wherein saidmicroscaled catalytic electrodes are either catalytic anode electrodesor catalytic cathode electrodes; at least one counter electrode inproximity to but not on said surface, wherein said counter electrodecomprises at least one catalytic cathode electrode if said microscaledcatalytic electrodes are catalytic anode electrodes, or said counterelectrode comprises at least one catalytic anode electrode if saidmicroscaled catalytic electrodes are catalytic cathode electrodes; meansfor collecting evolved hydrogen and/or oxygen gas; electrical poweringmeans for applying a voltage across said plurality of microscaledcatalytic electrodes and said at least one counter electrode; and acontainer for holding an aqueous electrolyte and housing said pluralityof microscaled catalytic electrodes and said at least one counterelectrode.
 2. The apparatus of claim 1, wherein saidlithographically-patternable substrate is a rigid semiconductingsubstrate.
 3. The apparatus of claim 2, wherein said semiconductingsubstrate is a silicon- containing substrate.
 4. The apparatus of claim1, wherein said means for collecting evolved hydrogen and/or oxygen gascomprises a canopy trapping device positioned over said plurality ofmicroscaled catalytic electrodes.
 5. The apparatus of claim 1, whereinsaid at least one counter electrode comprises a plurality of microscaledcatalytic counter electrodes embedded on a separatelithographically-patternable substrate.
 6. The apparatus of claim 5,further comprising means for collecting evolved hydrogen and oxygen gas,wherein said means comprises a canopy trapping device positioned oversaid plurality of microscaled catalytic electrodes and a separate canopytrapping device positioned over said plurality of microscaled catalyticcounter electrodes.
 7. The apparatus of claim 1, wherein said pluralityof microscaled catalytic electrodes and said at least one counterelectrode are not separated by an ion-permeable barrier between saidmicroscaled catalytic electrodes and said counter electrode.
 8. Theapparatus of claim 1, wherein said plurality of microscaled catalyticelectrodes and said at least one counter electrode are housed inseparate compartments, provided that means are included for allowingions to migrant between said compartments.
 9. The apparatus of claim 8,wherein said separate compartments are adjoined by a common wall,wherein said common wall includes at least one pore that traverses saidcommon wall.
 10. The apparatus of claim 9, wherein said common wall iscomprised of said at least one lithographically-patternable substratehaving said microscaled catalytic electrodes embedded thereon.
 11. Theapparatus of claim 10, wherein said lithographically-patternablesubstrate possesses a first surface on which is disposed a plurality ofmicroscaled catalytic anode electrodes, and a second surface on which isdisposed a plurality of microscaled catalytic cathode electrodes,wherein said first surface faces into a first compartment in whichoxygen is to be produced, and said second surface faces into a secondcompartment in which hydrogen is to be produced.
 12. The apparatus ofclaim 1, wherein said electrical powering means includeselectrically-conductive bond pads and wiring connected to saidelectrodes.
 13. The apparatus of claim 1, wherein said electricalpowering means comprises at least one receiving coil in electricalcommunication with said microscaled catalytic electrodes, wherein saidreceiving coil includes means for producing electrical power wirelesslyfrom a wireless transmission source.
 14. The apparatus of claim 13,wherein said electrical powering means further comprises a rectenna. 15.The apparatus of claim 1, wherein said electrical powering means furtherincludes circuitry for monitoring voltage and current levels of eachmicroscaled catalytic electrode.
 16. The apparatus of claim 15, whereinsaid electrical powering means further includes circuitry for settingvoltage and current levels of each microscaled catalytic electrode. 17.The apparatus of claim 1, wherein said electrical powering means furtherincludes superconducting wires for bringing electric current to themicroscaled catalytic electrodes.
 18. The apparatus of claim 1, whereinsaid microscaled catalytic electrodes and electrical powering means havebeen lithographically patterned onto said lithographically-patternablesubstrate.
 19. The apparatus of claim 18, wherein saidlithographically-patternable substrate is hermetically sealed, providedthat electrocatalytic surfaces of said microscaled catalytic electrodesare exposed.
 20. An apparatus for the electrolytic splitting of waterinto hydrogen and oxygen, the apparatus comprising: a firstlithographically-patternable substrate having a first surface, and aplurality of microscaled catalytic anode electrodes on said firstsurface; a second lithographically-patternable substrate having a secondsurface, and a plurality of microscaled catalytic cathode electrodes onsaid second surface; means for collecting evolved hydrogen and/or oxygengas; electrical powering means for applying a voltage across saidplurality of microscaled catalytic anode and cathode electrodes; and acontainer for holding an aqueous electrolyte and housing said pluralityof microscaled catalytic anode and cathode electrodes.
 21. The apparatusof claim 20, wherein said microscaled catalytic anode and cathodeelectrodes are not separated by an ion-permeable barrier.
 22. Theapparatus of claim 20, wherein said microscaled catalytic anode andcathode electrodes are separated by an ion-permeable barrier.
 23. Anapparatus for the electrolytic splitting of water into hydrogen andoxygen, the apparatus comprising: at least one rigid planar substratemade of a semiconducting composition, the at least one rigid planarsubstrate having a first surface and a second surface opposite the firstsurface; a plurality of microscaled catalytic anode electrodes disposedon said first surface; a plurality of microscaled catalytic cathodeelectrodes disposed on said second surface; at least one pore connectingsaid first and second surfaces; electrical powering means for applying avoltage across said plurality of microscaled catalytic anode and cathodeelectrodes; a first compartment that surrounds said microscaledcatalytic anode electrodes while excluding said microscaled catalyticcathode electrodes; a second compartment that surrounds said microscaledcatalytic cathode electrodes while excluding said microscaled catalyticanode electrodes; and means for collecting said hydrogen and oxygengases; wherein said rigid planar substrate functions as a common walladjoining said first and second compartments.
 24. An apparatus for theelectrolytic splitting of water into hydrogen and oxygen, the apparatuscomprising: at least one first rigid planar substrate made of asemiconducting composition, the at least one first rigid planarsubstrate having a first planar surface on which a plurality ofmicroscaled catalyst anode electrodes are disposed, and a second planarsurface opposite to said first planar surface; at least one second rigidplanar substrate made of a semiconducting composition, the at least onesecond rigid planar substrate having a first planar surface on which aplurality of microscaled catalytic cathode electrodes are disposed, anda second planar surface opposite to said first planar surface; a protonexchange membrane having first and second planar surfaces and sandwichedbetween said first and second rigid planar substrates, wherein saidfirst planar surface of said membrane is in physical contact with saidsecond planar surface of said first rigid planar substrate, and saidsecond planar surface of said membrane is in physical contact with saidsecond planar surface of said second rigid planar substrate; at leastone pore having a first section and a second section, wherein said firstand second pore sections are colinear, and said first section extendsfrom said membrane to said first planar surface of said first rigidplanar substrate, and said second pore section extends from saidmembrane to said first planar surface of said second rigid planarsubstrate; electrical powering means for applying a voltage across saidplurality of microscaled catalytic anode and cathode electrodes; a firstcompartment that surrounds said microscaled catalytic anode electrodeswhile excluding said microscaled catalytic cathode electrodes; a secondcompartment that surrounds said microscaled catalytic cathode electrodeswhile excluding said microscaled catalytic anode electrodes; and meansfor collecting evolved hydrogen and oxygen gases.
 25. An electrodedevice useful as an anode or a cathode in a water electrolysisapparatus, the electrode device comprising alithographically-patternable substrate having a surface, and a pluralityof microscaled catalytic electrodes on said surface.
 26. A method forproducing hydrogen and oxygen gases from the electrolytic splitting ofwater, the method comprising charging an electrolyzer with an aqueouselectrolyte, and electrically powering said electrolyzer to producehydrogen and oxygen gases, wherein said electrolyzer comprises theapparatus delineated in claim
 1. 27. A method for producing hydrogen andoxygen gases from the electrolytic splitting of water, the methodcomprising charging an electrolyzer with an aqueous electrolyte, andelectrically powering said electrolyzer to produce hydrogen and oxygengases, wherein said electrolyzer comprises the apparatus delineated inclaim
 20. 28. A method for producing hydrogen and oxygen gases from theelectrolytic splitting of water, the method comprising charging anelectrolyzer with an aqueous electrolyte, and electrically powering saidelectrolyzer to produce hydrogen and oxygen gases, wherein saidelectrolyzer comprises the apparatus delineated in claim
 23. 29. Amethod for producing hydrogen and oxygen gases from the electrolyticsplitting of water, the method comprising charging an electrolyzer withan aqueous electrolyte, and electrically powering said electrolyzer toproduce hydrogen and oxygen gases, wherein said electrolyzer comprisesthe apparatus delineated in claim
 24. 30. The method of claim 26,wherein said electrolyzer is powered by a renewable energy source. 31.The method of claim 30, wherein said renewable energy source comprisessolar energy.
 32. The method of claim 30, wherein said renewable energysource comprises wind energy.
 33. The method of claim 26, wherein saidelectrolyzer is electrically powered by nuclear energy.
 34. The methodof claim 26, wherein said electrolysis method is coupled to a processthat utilizes hydrogen or oxygen gas.
 35. The method of claim 34,wherein said process is a Fischer-Tropsch process for the synthesis ofliquid hydrocarbons.
 36. The method of claim 34, wherein said process isa petroleum refining process.
 37. The method of claim 36, wherein saidpetroleum refining process is a hydrodealkylation, hydrodesulfurization,or hydrocracking process.
 38. The method of claim 34, wherein saidprocess is a Haber process.
 39. The method of claim 34, wherein saidprocess is a hydrogenation process.
 40. A method for producing chlorinegas and/or a metal hydroxide by a chloralkali process, the methodcomprising charging the water electrolyzer delineated in claim 1 with anaqueous metal-chloride salt electrolyte, and electrically powering saidelectrolyzer to produce chlorine gas at the catalytic anode electrode ofthe water electrolyzer and hydrogen gas and a metal hydroxide at thecatalytic cathode electrode of the water electrolyzer.
 41. A method forproducing chlorine gas and/or a metal hydroxide by a chloralkaliprocess, the method comprising charging the water electrolyzerdelineated in claim 20 with an aqueous metal-chloride salt electrolyte,and electrically powering said electrolyzer to produce chlorine gas atsaid plurality of microscaled catalytic anode electrodes of the waterelectrolyzer and hydrogen gas and a metal hydroxide at said plurality ofmicroscaled catalytic cathode electrodes of the water electrolyzer. 42.A method for producing chlorine gas and/or a metal hydroxide by achloralkali process, the method comprising charging the waterelectrolyzer delineated in claim 23 with an aqueous metal-chloride saltelectrolyte, and electrically powering said electrolyzer to producechlorine gas at said plurality of microscaled catalytic anode electrodesof the water electrolyzer and hydrogen gas and a metal hydroxide at saidplurality of microscaled catalytic cathode electrodes of the waterelectrolyzer.
 43. A method for producing chlorine gas and/or a metalhydroxide by a chloralkali process, the method comprising charging thewater electrolyzer delineated in claim 24 with an aqueous metal-chloridesalt electrolyte, and electrically powering said electrolyzer to producechlorine gas at said plurality of microscaled catalytic anode electrodesof the water electrolyzer and hydrogen gas and a metal hydroxide at saidplurality of microscaled catalytic cathode electrodes of the waterelectrolyzer.
 44. The method of claim 40, further comprising anion-permeable membrane separating said catalytic anode electrode andcatalytic cathode electrode.
 45. The method of claim 40, wherein saidmetal chloride salt comprises sodium chloride and said metal hydroxidecomprises sodium hydroxide.
 46. An apparatus for the electrolyticsplitting of water into hydrogen and/or oxygen, the apparatuscomprising: a bulk catalytic electrode containing thereon a plurality ofmicroscopic catalytic hot spots on a surface of said bulk catalyticelectrode, wherein said bulk catalytic electrode is either a catalyticanode or catalytic cathode; a counter electrode; means for collectingevolved hydrogen and/or oxygen gas; electrical powering means forapplying a voltage across said bulk catalytic electrode and counterelectrode; and a container for holding an aqueous electrolyte andhousing said bulk catalytic electrode and counter electrode.
 47. Anapparatus for the electrolytic splitting of water into hydrogen and/oroxygen, the apparatus comprising: a bulk catalytic electrode having onits surface an insulating layer containing a plurality of microscopicholes therein, wherein said bulk catalytic electrode is either acatalytic anode or catalytic cathode, and said holes permit said bulkcatalytic electrode to be exposed to electrolyte only at said holes; acounter electrode; means for collecting evolved hydrogen and/or oxygengas; electrical powering means for applying a voltage across said bulkcatalytic electrode and counter electrode; and a container for holdingan aqueous electrolyte and housing said bulk catalytic electrode andcounter electrode.